Etextbook 978 0321971371 organic chemistry

eTextbook 978-0321971371 Organic Chemistry Visit to download the full and correct content document: https://ebookmass.com/product/etextbook-978-0321971371-organic-chemistry/

Contents

vii

4-9 4-10 4-11 4-12 4-13 4-14

Activation Energy and the Temperature Dependence of Rates 171 Transition States 172 Rates of Multistep Reactions 174 Temperature Dependence of Halogenation 175 Selectivity in Halogenation 176 Hammond’s Postulate 182 PROBLEM-SOLVING STRATEGY: Proposing Reaction Mechanisms 183 4-15 Radical Inhibitors 186 4-16 Reactive Intermediates 187 Summary: Reactive Intermediates 194 Essential Terms 194 Study Problems 197

5 STEREOCHEMISTRY 201 5-1 5-2 5-3 5-4 5-5 5-6 5-7 5-8 5-9 5-10

Introduction 201 Chirality 202 (R) and (S) Nomenclature of Asymmetric Carbon Atoms 208 Optical Activity 213 Biological Discrimination of Enantiomers 218 Racemic Mixtures 219 Enantiomeric Excess and Optical Purity 220 Chirality of Conformationally Mobile Systems 221 Chiral Compounds Without Asymmetric Atoms 224 Fischer Projections 226 Summary: Fischer Projections and Their Use 230 5-11 Diastereomers 230 Summary: Types of Isomers 232 5-12 Stereochemistry of Molecules with Two or More Asymmetric Carbons 233 5-13 Meso Compounds 233 5-14 Absolute and Relative Configuration 235 5-15 Physical Properties of Diastereomers 237 5-16 Resolution of Enantiomers 238 Essential Terms 241 Study Problems 244

6 ALKYL HALIDES; NUCLEOPHILIC SUBSTITUTION 247 6-1 Introduction 247 6-2 Nomenclature of Alkyl Halides 248 H3C O Common Uses of Alkyl Halides 250 Cl 6-3 Br H3C 6-4 Structure CH3 of Alkyl Halides 252 6-5 kumepaloxane Physical Properties of Alkyl Halides 253 6-6 Preparation of Alkyl Halides 255 cymbal bubble snail Haminoea cymbalum

Summary: Methods for Preparing Alkyl Halides 259 6-7 Reactions of Alkyl Halides: Substitution and Elimination 260

viii

Contents

6-8 6-9

Bimolecular Nucleophilic Substitution: The SN2 Reaction 261 Generality of the SN2 Reaction 263 Summary: SN2 Reactions of Alkyl Halides 264 6-10 Factors Affecting SN2 Reactions: Strength of the Nucleophile 265 Summary: Trends in Nucleophilicity 266 6-11 Reactivity of the Substrate in SN2 Reactions 269 6-12 Stereochemistry of the SN2 Reaction 273 6-13 Unimolecular Nucleophilic Substitution: The SN1 Reaction 275 6-14 Stereochemistry of the SN1 Reaction 279 6-15 Rearrangements in SN1 Reactions 281 6-16 Comparison of SN1 and SN2 Reactions 284 Summary: Nucleophilic Substitutions 286 Summary: Reactions of Alkyl Halides 287 Essential Terms 288 Study Problems 291

7 STRUCTURE AND SYNTHESIS OF ALKENES; ELIMINATION 296 7-1 7-2 7-3 7-4 7-5

squalene

Introduction 296 The Orbital Description of the Alkene Double Bond 297 Elements of Unsaturation 299 Nomenclature of Alkenes 301 Nomenclature of Cis-Trans Isomers 303 Summary: Rules for Naming Alkenes 305 7-6 Commercial Importance of Alkenes 306 7-7 Physical Properties of Alkenes 308 7-8 Stability of Alkenes 310 7-9 Formation of Alkenes by Dehydrohalogenation of Alkyl Halides 318 7-10 Unimolecular Elimination: The E1 Reaction 319 Summary: Carbocation Reactions 323 7-11 Positional Orientation of Elimination: Zaitsev’s Rule 324 7-12 Bimolecular Elimination: The E2 Reaction 326 7-13 Bulky Bases in E2 Eliminations; Hofmann Orientation 328 7-14 Stereochemistry of the E2 Reaction 329 7-15 E2 Reactions in Cyclohexane Systems 332 7-16 Comparison of E1 and E2 Elimination Mechanisms 334 Summary: Elimination Reactions 335 7-17 Competition Between Substitutions and Eliminations 336 Summary: Substitution and Elimination Reactions of Alkyl Halides 338 PROBLEM-SOLVING STRATEGY: Predicting Substitutions and Eliminations 340 7-18 Alkene Synthesis by Dehydration of Alcohols 341 7-19 Alkene Synthesis by High-Temperature Industrial Methods 344 PROBLEM-SOLVING STRATEGY: Proposing Reaction Mechanisms 346 Summary: Methods for Synthesis of Alkenes 349 Essential Terms 350 Study Problems 353

Contents

8 REACTIONS OF ALKENES 359 8-1 8-2 8-3 8-4 8-5 8-6 8-7 8-8 8-9 8-10 8-11 8-12 8-13 8-14 8-15 8-16 8-17

Reactivity of the Carbon–Carbon Double Bond 359 Electrophilic Addition to Alkenes 360 Addition of Hydrogen Halides to Alkenes 362 Addition of Water: Hydration of Alkenes 370 Hydration by Oxymercuration–Demercuration 372 Alkoxymercuration–Demercuration 375 Hydroboration of Alkenes 376 Addition of Halogens to Alkenes 382 Formation of Halohydrins 385 Catalytic Hydrogenation of Alkenes 389 Addition of Carbenes to Alkenes 391 Epoxidation of Alkenes 393 Acid-Catalyzed Opening of Epoxides 395 Syn Dihydroxylation of Alkenes 398 Oxidative Cleavage of Alkenes 400 Polymerization of Alkenes 403 Olefin Metathesis 407 PROBLEM-SOLVING STRATEGY: Organic Synthesis 410 Summary: Reactions of Alkenes 412 Summary: Electrophilic Additions to Alkenes 415 Summary: Oxidation and Cyclopropanation Reactions of Alkenes 416 Essential Terms 417 Study Problems 421

9 ALKYNES 428 9-1 9-2 9-3 9-4 9-5 9-6 9-7 9-8

Introduction 428 Nomenclature of Alkynes 429 Physical Properties of Alkynes 431 Commercial Importance of Alkynes 431 Electronic Structure of Alkynes 433 Acidity of Alkynes; Formation of Acetylide Ions 434 Synthesis of Alkynes from Acetylides 436 Synthesis of Alkynes by Elimination Reactions 439 Summary: Syntheses of Alkynes 441 9-9 Addition Reactions of Alkynes 441 9-10 Oxidation of Alkynes 450 PROBLEM-SOLVING STRATEGY: Multistep Synthesis 452 Summary: Reactions of Alkynes 454 Summary: Reactions of Terminal Alkynes 455 Essential Terms 456 Study Problems 457

ix

x

Contents

10 STRUCTURE AND SYNTHESIS OF ALCOHOLS 460

O

l

l-menthone

10-1 10-2 10-3 10-4 10-5 10-6 10-7

Introduction 460 Structure and Classification of Alcohols 460 Nomenclature of Alcohols and Phenols 461 Physical Properties of Alcohols 466 Commercially Important Alcohols 468 Acidity of Alcohols and Phenols 470 Synthesis of Alcohols: Introduction and Review 474 Summary: Previous Alcohol Syntheses 474 10-8 Organometallic Reagents for Alcohol Synthesis 475 10-9 Reactions of Organometallic Compounds 478 Summary: Grignard Reactions 484 10-10 Side Reactions of Organometallic Reagents: Reduction of Alkyl Halides 486 10-11 Reduction of the Carbonyl Group: Synthesis of 1° and 2° Alcohols 489 Summary: Reactions of LiAIH4 and NaBH4 491 Summary: Alcohol Syntheses by Nucleophilic Additions to Carbonyl Groups 492 10-12 Thiols (Mercaptans) 494 Summary: Synthesis of Alcohols from Carbonyl Compounds 497 Essential Terms 497 Study Problems 499

11 REACTIONS OF ALCOHOLS 505 11-1 11-2 11-3 11-4 11-5

Oxidation States of Alcohols and Related Functional Groups 506 Oxidation of Alcohols 507 O O CH Additional Methods for Oxidizing Alcohols 511 Biological Oxidation of Alcohols 513 H H C C Alcohols as Nucleophiles and Electrophiles; Formation of Tosylates 515 CH (CH ) (CH ) CH OH Summary: SN2 Reactions of Tosylate Esters 517 11-6 Reduction of Alcohols 518 11-7 Reactions of Alcohols with Hydrohalic Acids 519 11-8 Reactions of Alcohols with Phosphorus Halides 524 11-9 Reactions of Alcohols with Thionyl Chloride 525 11-10 Dehydration Reactions of Alcohols 527 PROBLEM-SOLVING STRATEGY: Proposing Reaction Mechanisms 531 11-11 Unique Reactions of Diols 534 11-12 Esterification of Alcohols 536 11-13 Esters of Inorganic Acids 537 11-14 Reactions of Alkoxides 540 PROBLEM-SOLVING STRATEGY: Multistep Synthesis 543 Summary: Reactions of Alcohols 546 Summary: Reactions of Alcohols: O ¬ H Cleavage 548 Summary: Reactions of Alcohols: C ¬ O Cleavage 548 Essential Terms 549 Study Problems 551 isopentyl acetate

3

2 7

2 9

(Z ) -eicos-11-en-1-ol

3

2

Contents

12 INFRARED SPECTROSCOPY AND MASS SPECTROMETRY 556 12-1 12-2 12-3 12-4 12-5 12-6 12-7 12-8 12-9 12-10 12-11 12-12 12-13 12-14

Introduction 556 The Electromagnetic Spectrum 557 The Infrared Region 558 Molecular Vibrations 559 IR-Active and IR-Inactive Vibrations 561 Measurement of the IR Spectrum 562 Infrared Spectroscopy of Hydrocarbons 565 Characteristic Absorptions of Alcohols and Amines 570 Characteristic Absorptions of Carbonyl Compounds 571 Characteristic Absorptions of C ¬ N Bonds 576 Simplified Summary of IR Stretching Frequencies 578 Reading and Interpreting IR Spectra (Solved Problems) 580 Introduction to Mass Spectrometry 584 Determination of the Molecular Formula by Mass Spectrometry 587 12-15 Fragmentation Patterns in Mass Spectrometry 590 Summary: Common Fragmentation Patterns 596 Essential Terms 597 Study Problems 599

13 NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 607 13-1 13-2 13-3 13-4 13-5 13-6 13-7 13-8

Introduction 607 Theory of Nuclear Magnetic Resonance 608 Magnetic Shielding by Electrons 610 The NMR Spectrometer 612 The Chemical Shift 613 The Number of Signals 620 Areas of the Peaks 622 Spin-Spin Splitting 625 PROBLEM-SOLVING STRATEGY: Drawing an NMR Spectrum 630 13-9 Complex Splitting 634 13-10 Stereochemical Nonequivalence of Protons 637 13-11 Time Dependence of NMR Spectroscopy 640 PROBLEM-SOLVING STRATEGY: Interpreting Proton NMR Spectra 643 13-12 Carbon-13 NMR Spectroscopy 648 13-13 Interpreting Carbon NMR Spectra 656 13-14 Nuclear Magnetic Resonance Imaging 658 PROBLEM-SOLVING STRATEGY: Spectroscopy Problems 659 Essential Terms 663 Study Problems 665

xi

xii

Contents

14 ETHERS, EPOXIDES, AND THIOETHERS 672 14-1 14-2 14-3 14-4 14-5 14-6 14-7

OH O

O

CH2

OH OH

15

O alizarin

CH

CH2

O

Introduction 672 Physical Properties of Ethers 673 Nomenclature of Ethers 677 Spectroscopy of Ethers 680 The Williamson Ether Synthesis 682 Synthesis of Ethers by Alkoxymercuration–Demercuration 684 Industrial Synthesis: Bimolecular Condensation of Alcohols 684 Summary: Syntheses of Ethers (Review) 685 14-8 Cleavage of Ethers by HBr and HI 686 Autoxidation of Ethers 688 n 14-9 Summary: Reactions of Ethers 689 14-10 Thioethers (Sulfides) and Silyl Ethers 689 14-11 Synthesis of Epoxides 693 Summary: Epoxide Syntheses 696 14-12 Acid-Catalyzed Ring Opening of Epoxides 696 14-13 Base-Catalyzed Ring Opening of Epoxides 700 14-14 Orientation of Epoxide Ring Opening 702 Summary: Orientation of Epoxide Ring Opening 703 14-15 Reactions of Epoxides with Grignard and Organolithium Reagents 704 14-16 Epoxy Resins: The Advent of Modern Glues 705 Summary: Reactions of Epoxides 707 Essential Terms 707 Study Problems 710

ONJUGATED SYSTEMS, ORBITAL SYMMETRY, AND C ULTRAVIOLET SPECTROSCOPY 716 15-1 15-2 15-3 15-4 15-5 15-6

Introduction 716 Stabilities of Dienes 717 Molecular Orbital Picture of a Conjugated System 718 Allylic Cations 723 1,2- and 1,4-Addition to Conjugated Dienes 724 Kinetic Versus Thermodynamic Control in the Addition of

HBr to Buta-1,3-diene 726 15-7 Allylic Radicals 728 15-8 Molecular Orbitals of the Allylic System 730 15-9 Electronic Configurations of the Allyl Radical, Cation, and Anion 732 15-10 SN2 Displacement Reactions of Allylic Halides and Tosylates 733 15-11 The Diels–Alder Reaction 734 15-12 The Diels–Alder as an Example of a Pericyclic Reaction 743 15-13 Ultraviolet Absorption Spectroscopy 746 15-14 Colored Organic Compounds 752 15-15 UV-Visible Analysis in Biology and Medicine 754 Essential Terms 756 Study Problems 759

Contents

16 AROMATIC COMPOUNDS 764

N

16-1 16-2 16-3 16-4 16-5 16-6 16-7 16-8 16-9 16-10 16-11 16-12 16-13 16-14 16-15

Introduction: The Discovery of Benzene 764 The Structure and Properties of Benzene 765 The Molecular Orbitals of Benzene 769 The Molecular Orbital Picture of Cyclobutadiene 772 Aromatic, Antiaromatic, and Nonaromatic Compounds 773 Hückel’s Rule 774 Molecular Orbital Derivation of Hückel’s Rule 776 Aromatic Ions 777 Heterocyclic Aromatic Compounds 783 Polynuclear Aromatic Hydrocarbons 787 Aromatic Allotropes of Carbon 789 Fused Heterocyclic Compounds 791 Nomenclature of Benzene Derivatives 792 Physical Properties of Benzene and Its Derivatives 794 Spectroscopy of Aromatic Compounds 796 Essential Terms 798 Study Problems 800

N

O

O

n

Zylon®

17 REACTIONS OF AROMATIC COMPOUNDS 809 17-1 17-2 17-3 17-4 17-5 17-6

NO2

HNO3 H2SO4

R alkylbenzene

NO2

or

R

R

NH2

Fe HCl(aq)

or

R

alkylnitrobenzene

alkylated anilines

aniline dyes

H2SO4

Electrophilic Aromatic Substitution 809 Halogenation of Benzene 811 Nitration of Benzene 813 Sulfonation of Benzene 814 Nitration of Toluene: The Effect of Alkyl Substitution 817 Activating, Ortho, Para-Directing Substituents 819 Summary: Activating, Ortho, Para-Directors 822 17-7 Deactivating, Meta-Directing Substituents 822 NH R

Summary: Deactivating, Meta-Directors 825 17-8 Halogen Substituents: Deactivating, but Ortho, Para-Directing 826 Summary: Directing Effects of Substituents 827 17-9 Effects of Multiple Substituents on Electrophilic Aromatic

Substitution 827 17-10 The Friedel–Crafts Alkylation 830 17-11 The Friedel–Crafts Acylation 835 Summary: Comparison of Friedel–Crafts Alkylation and Acylation 837 17-12 Nucleophilic Aromatic Substitution 839 17-13 Aromatic Substitutions Using Organometallic Reagents 843 17-14 Addition Reactions of Benzene Derivatives 849 17-15 Side-Chain Reactions of Benzene Derivatives 852 17-16 Reactions of Phenols 856 PROBLEM-SOLVING STRATEGY: Synthesis Using Electrophilic Aromatic Substitution 859 Summary: Reactions of Aromatic Compounds 863 2

xiii

xiv

Contents

Summary: Electrophilic Aromatic Substitution of Benzene 866 Summary: Substitutions of Aryl Halides 866 Essential Terms 867 Study Problems 870

18 KETONES AND ALDEHYDES 876 18-1 18-2 18-3 18-4 18-5 18-6 18-7 18-8 18-9 canthaxanthin 18-10

Carbonyl Compounds 876 Structure of the Carbonyl Group 877 Nomenclature of Ketones and Aldehydes 878 Physical Properties of Ketones and Aldehydes 880 Spectroscopy of Ketones and Aldehydes 882 Industrial Importance of Ketones and Aldehydes 888 O Review of Syntheses of Ketones and Aldehydes 889 Synthesis of Ketones from Carboxylic Acids 893 Synthesis of Ketones and Aldehydes from Nitriles 893 Synthesis of Aldehydes and Ketones from Acid Chlorides and Esters 895 Summary: Syntheses of Ketones and Aldehydes 897 18-11 Reactions of Ketones and Aldehydes: Introduction to Nucleophilic Addition 898 18-12 Hydration of Ketones and Aldehydes 902 18-13 Formation of Cyanohydrins 904 18-14 Formation of Imines 906 18-15 Condensations with Hydroxylamine and Hydrazines 909 Summary: Condensations of Amines with Ketones and Aldehydes 910 18-16 Formation of Acetals 911 PROBLEM-SOLVING STRATEGY: Proposing Reaction Mechanisms 915 18-17 Use of Acetals as Protecting Groups 916 18-18 The Wittig Reaction 918 18-19 Oxidation of Aldehydes 921 18-20 Reductions of Ketones and Aldehydes 922 Summary: Reactions of Ketones and Aldehydes 925 Summary: Nucleophilic Addition Reactions of Aldehydes and Ketones 927 Essential Terms 928 Study Problems 931

O

19 AMINES 941

O– N+

H3C

CH3 CH3

trimethylamine oxide (TMAO)

N

H3 C

CH3 CH3

trimethylamine

+

1 2 O2

19-1 19-2 19-3 19-4 19-5 19-6 19-7 19-8 19-9 19-10

Introduction 941 Nomenclature of Amines 942 Structure of Amines 945 Physical Properties of Amines 947 Basicity of Amines 948 Factors that Affect Amine Basicity 950 Salts of Amines 952 Spectroscopy of Amines 954 Reactions of Amines with Ketones and Aldehydes (Review) 958 Aromatic Substitution of Arylamines and Pyridine 958

Contents

19-11 19-12 19-13 19-14 19-15 19-16 19-17

Alkylation of Amines by Alkyl Halides 962 Acylation of Amines by Acid Chlorides 963 Formation of Sulfonamides 965 Amines as Leaving Groups: The Hofmann Elimination 967 Oxidation of Amines; The Cope Elimination 970 Reactions of Amines with Nitrous Acid 973 Reactions of Arenediazonium Salts 975 Summary: Reactions of Amines 978 19-18 Synthesis of Amines by Reductive Amination 980 19-19 Synthesis of Amines by Acylation–Reduction 982 19-20 Syntheses Limited to Primary Amines 984 Summary: Synthesis of Amines 988 Essential Terms 989 Study Problems 992

20 CARBOXYLIC ACIDS 1002 20-1H Introduction 1002 O Nomenclature of Carboxylic Acids 1003 H 20-2 O C Structure 20-3 and Physical Properties of Carboxylic Acids 1006 H H 3C C 20-4 O Acidity of Carboxylic Acids 1007 (S)-lactic acid 20-5 Salts of Carboxylic Acids 1011 20-6 Commercial Sources of Carboxylic Acids 1013 20-7 Spectroscopy of Carboxylic Acids 1015 20-8 Synthesis of Carboxylic Acids 1019 Summary: Syntheses of Carboxylic Acids 1021 20-9 Reactions of Carboxylic Acids and Derivatives; Nucleophilic Acyl

Substitution 1022 (S)-lactic acid 20-10 Condensation of Acids with Alcohols: The Fischer Esterification 1024 20-11 Esterification Using Diazomethane 1028 20-12 Condensation of Acids with Amines: Direct Synthesis of Amides 1028 20-13 Reduction of Carboxylic Acids 1029 20-14 Alkylation of Carboxylic Acids to Form Ketones 1031 20-15 Synthesis and Use of Acid Chlorides 1031 Summary: Reactions of Carboxylic Acids 1034, 1035 Essential Terms 1036 Study Problems 1037

21 CARBOXYLIC ACID DERIVATIVES 1043 21-1 21-2 21-3 21-4 21-5

PhOCH2

O

H

C

N O penicillin V a penicillin

S N

CH3 CH3

COOH

Ph

CH NH2

O

H

C

N O

OH S N COOH ®

cephalexin (Keflex ) a cephalosporin

NH

CH3CH CH3

O

N

SCH2CH2N H

COOH ®

imipenem (Primaxin ) a carbapenem

C

H

Introduction 1043 Structure and Nomenclature of Acid Derivatives 1044 Physical Properties of Carboxylic Acid Derivatives 1051 Spectroscopy of Carboxylic Acid Derivatives 1053 Interconversion of Acid Derivatives by Nucleophilic Acyl Substitution 1060 21-6 Transesterification 1069 PROBLEM-SOLVING STRATEGY: Proposing Reaction Mechanisms 1070

xv

xvi

Contents

21-7 21-8 21-9 21-10 21-11 21-12 21-13 21-14 21-15 21-16

Hydrolysis of Carboxylic Acid Derivatives 1073 Reduction of Acid Derivatives 1078 Reactions of Acid Derivatives with Organometallic Reagents 1081 Summary of the Chemistry of Acid Chlorides 1083 Summary of the Chemistry of Anhydrides 1085 Summary of the Chemistry of Esters 1088 Summary of the Chemistry of Amides 1091 Summary of the Chemistry of Nitriles 1094 Thioesters 1095 Esters and Amides of Carbonic Acid 1097 Essential Terms 1099 Summary: Reactions of Acid Chlorides 1100 Study Problems 1103

22

ONDENSATIONS AND ALPHA SUBSTITUTIONS OF CARBONYL C ­COMPOUNDS 1112 22-1 22-2 22-3 22-4 22-5 22-6 22-7 22-8 22-9

Introduction 1112 Enols and Enolate Ions 1114 Alkylation of Enolate Ions 1117 Formation and Alkylation of Enamines 1119 Alpha Halogenation of Ketones 1121 Alpha Bromination of Acids: The HVZ Reaction 1127 The Aldol Condensation of Ketones and Aldehydes 1128 Dehydration of Aldol Products 1132 Crossed Aldol Condensations 1133 PROBLEM-SOLVING STRATEGY: Proposing Reaction Mechanisms 1134 22-10 Aldol Cyclizations 1136 22-11 Planning Syntheses Using Aldol Condensations 1137 22-12 The Claisen Ester Condensation 1139 22-13 The Dieckmann Condensation: A Claisen Cyclization 1142 22-14 Crossed Claisen Condensations 1143 22-15 Syntheses Using b-Dicarbonyl Compounds 1146 22-16 The Malonic Ester Synthesis 1148 22-17 The Acetoacetic Ester Synthesis 1151 22-18 Conjugate Additions: The Michael Reaction 1154 22-19 The Robinson Annulation 1158 PROBLEM-SOLVING STRATEGY: Proposing Reaction Mechanisms 1159 Summary: Enolate Additions and Condensations 1161 Summary: Reactions of Stabilized Carbanions 1163 Essential Terms 1163 Study Problems 1166

Contents

23 CARBOHYDRATES AND NUCLEIC ACIDS 1172

OH

CH2OH H

H

O

HO

O H H

NH O

C

H

CH3

N-acetyl-D-galactosamine

23-1 23-2 23-3 23-4 23-5 23-6 23-7 OH CH2OH H 23-8 O H 23-9 HO O H OH 23-10 H H 23-11 D-galactose

Introduction 1172 Classification of Carbohydrates 1173 Monosaccharides 1174 Cyclic Structures of Monosaccharides 1178 Anomers of Monosaccharides; Mutarotation 1182 Reactions of Monosaccharides: Reduction 1185 Oxidation of Monosaccharides; Reducing Sugars 1186 Nonreducing Sugars: Formation of Glycosides 1188 Ether and Ester Formation 1190 Chain Shortening: The Ruff Degradation 1193 Chain Lengthening: The Kiliani–Fischer Synthesis 1194 Summary: Reactions of Sugars 1196 23-12 Disaccharides 1198 23-13 Polysaccharides 1203 23-14 Nucleic Acids: Introduction 1206 23-15 Ribonucleosides and Ribonucleotides 1208 23-16 The Structures of RNA and DNA 1210 23-17 Additional Functions of Nucleotides 1214 Essential Terms 1216 Study Problems 1219

24 AMINO ACIDS, PEPTIDES, AND PROTEINS 1222 24-1 24-2 24-3 24-4 24-5

Introduction 1222 Structure and Stereochemistry of the a-Amino Acids 1223 Acid–Base Properties of Amino Acids 1227 Isoelectric Points and Electrophoresis 1229 Synthesis of Amino Acids 1231 Summary: Syntheses of Amino Acids 1234 24-6 Resolution of Amino Acids 1234 24-7 Reactions of Amino Acids 1235 Summary: Reactions of Amino Acids 1238 24-8 Structure and Nomenclature of Peptides and Proteins 1238 24-9 Peptide Structure Determination 1242 24-10 Laboratory Peptide Synthesis 1247 24-11 Classification of Proteins 1253 24-12 Levels of Protein Structure 1254 24-13 Protein Denaturation 1256 Essential Terms 1259 Study Problems 1261

xvii

xviii

Contents

25 LIPIDS 1265 25-1 25-2 25-3 25-4 25-5 25-6 25-7 25-8

Introduction 1265 Waxes 1266 Triglycerides 1266 Saponification of Fats and Oils: Soaps and Detergents 1270 Phospholipids 1273 Steroids 1275 Prostaglandins 1278 Terpenes 1279 Essential Terms 1282 Study Problems 1283

26 SYNTHETIC POLYMERS 1286 26-1 26-2 26-3 26-4 26-5 26-6 26-7 26-8 26-9

Introduction 1286 Chain-Growth Polymers 1287 Stereochemistry of Polymers 1293 Stereochemical Control of Polymerization: Ziegler–Natta Catalysts 1294 Natural and Synthetic Rubbers 1295 Copolymers of Two or More Monomers 1297 Step-Growth Polymers 1297 Polymer Structure and Properties 1301 Recycling of Plastics 1303 Essential Terms 1304 Study Problems 1306

APPENDICES 1308 1A 1B 1C 2A 2B 3A 3B 4 5

NMR: Spin-Spin Coupling Constants 1308 NMR: Proton Chemical Shifts 1309 NMR: 13C Chemical Shifts in Organic Compounds 1311 IR: Characteristic Infrared Group Frequencies 1312 IR: Characteristic Infrared Absorptions of Functional Groups 1315 Methods and Suggestions for Proposing Mechanisms 1317 Suggestions for Developing Multistep Syntheses 1319 pKa Values for Representative Compounds 1320 Summary of Organic Nomenclature 1322

Brief Answers to Selected Problems A1 Photo Credits PC1 Index

I1

Contents

MECHANISMS CHAPTER 4 CHAPTER 6

Free-Radical Halogenation 159 Allylic Bromination 258 The SN2 Reaction 263 Inversion of Configuration in the SN2 Reaction 273 The SN1 Reaction 276 Racemization in the SN1 Reaction 281 Hydride Shift in an SN1 Reaction 282 Methyl Shift in an SN1 Reaction 283

CHAPTER 7

The E1 Reaction 319 Rearrangement in an E1 Reaction 322 The E2 Reaction 326 Stereochemistry of the E2 Reaction 331 Acid-Catalyzed Dehydration of an Alcohol 342

CHAPTER 8

Electrophilic Addition to Alkenes 361 Ionic Addition of HX to an Alkene 363 Free-Radical Addition of HBr to Alkenes 366 Acid-Catalyzed Hydration of an Alkene 370 Oxymercuration of an Alkene 373 Hydroboration of an Alkene 378 Addition of Halogens to Alkenes 383 Formation of Halohydrins 386 Epoxidation of Alkenes 394 Acid-Catalyzed Opening of Epoxides 395 Olefin Metathesis 409

CHAPTER 9

Metal–Ammonia Reduction of an Alkyne 444 Acid-Catalyzed Keto–Enol Tautomerism 448 Base-Catalyzed Keto–Enol Tautomerism 449

CHAPTER 10

Grignard Reactions 478 Hydride Reduction of a Carbonyl Group 489

CHAPTER 11

Reaction of a Tertiary Alcohol with HBr (SN1) 519 Reaction of a Primary Alcohol with HBr (SN2) 520 Reaction of Alcohols with PBr3 525 (Review): Acid-Catalyzed Dehydration of an Alcohol 527 The Pinacol Rearrangement 535 The Williamson Ether Synthesis 541

xix

xx

Contents

MECHANISMS (continued) CHAPTER 14

Cleavage of an Ether by HBr or HI 686 Acid-Catalyzed Opening of Epoxides in Water 697 Acid-Catalyzed Opening of an Epoxide in an Alcohol Solution 698 Base-Catalyzed Opening of Epoxides 701

CHAPTER 15

1,2- and 1,4-Addition to a Conjugated Diene 725 Free-Radical Allylic Bromination 728 The Diels–Alder Reaction 734

CHAPTER 17

Electrophilic Aromatic Substitution 810 Bromination of Benzene 811 Nitration of Benzene 813 Sulfonation of Benzene 815 Friedel–Crafts Alkylation 831 Friedel–Crafts Acylation 836 Nucleophilic Aromatic Substitution (Addition–Elimination) 840 Nucleophilic Aromatic Substitution (Benzyne Mechanism) 842 The Suzuki Reaction 849 The Birch Reduction 851

CHAPTER 18

Nucleophilic Additions to Carbonyl Groups 901 Hydration of Ketones and Aldehydes 903 Formation of Cyanohydrins 905 Formation of Imines 907  Formation of Acetals 912  The Wittig Reaction 919 Wolff–Kishner Reduction 924

CHAPTER 19

Electrophilic Aromatic Substitution of Pyridine 960 Nucleophilic Aromatic Substitution of Pyridine 961 Acylation of an Amine by an Acid Chloride 964 Hofmann Elimination 967 The Cope Elimination of an Amine Oxide 971 Diazotization of an Amine 973

CHAPTER 20

Nucleophilic Acyl Substitution in the Basic Hydrolysis of an Ester 1023 Fischer Esterification 1024  Esterification Using Diazomethane 1028 

Contents

MECHANISMS (continued) CHAPTER 21

Addition–Elimination Mechanism of Nucleophilic Acyl Substitution 1060 Conversion of an Acid Chloride to an Anhydride 1063 Conversion of an Acid Chloride to an Ester 1064 Conversion of an Acid Chloride to an Amide 1064 Conversion of an Acid Anhydride to an Ester 1065 Conversion of an Acid Anhydride to an Amide 1065 Conversion of an Ester to an Amide (Ammonolysis of an Ester) 1066 Transesterification 1072 Saponification of an Ester 1074 Basic Hydrolysis of an Amide 1076 Acidic Hydrolysis of an Amide 1076 Base-Catalyzed Hydrolysis of a Nitrile 1078 Hydride Reduction of an Ester 1079 Reduction of an Amide to an Amine 1080 Reaction of an Ester with Two Moles of a Grignard Reagent 1082

CHAPTER 22

Alpha Substitution 1113 Addition of an Enolate to Ketones and Aldehydes (a Condensation) 1113 Substitution of an Enolate on an Ester (a Condensation) 1113 Base-Catalyzed Keto–Enol Tautomerism 1114 Acid-Catalyzed Keto–Enol Tautomerism 1115 Base-Promoted Halogenation 1122 Final Steps of the Haloform Reaction 1124 Acid-Catalyzed Alpha Halogenation 1126 Base-Catalyzed Aldol Condensation 1129  Acid-Catalyzed Aldol Condensation 1131 Base-Catalyzed Dehydration of an Aldol 1132  The Claisen Ester Condensation 1139  1,2-Addition and 1,4-Addition (Conjugate Addition) 1154

CHAPTER 23

Formation of a Cyclic Hemiacetal 1178

CHAPTER 26

Free-Radical Polymerization 1289 Cationic Polymerization 1291 Anionic Polymerization 1293

xxi

New to This Edition 1 NEW! Expanded coverage of Acid/Base Chemistry in chapter 2 and separation of the chapter on Substitution and Elimination into two distinct chapters allow students to build upon their existing knowledge and move through their first mechanisms with greater clarity and with more opportunities to test and apply their understanding without getting overwhelmed by organic chemistry.

New problem-solving strategy spreads have been added to both corresponding chapters for additional support.

2 NEW! Reaction Starbursts/Reaction Maps

appear before the end of every ‘reaction-based’ chapter to help students better understand and mentally organize reactive similarities and distinctions.

3 NEW! Visual Guides to Organic Reactions place

the reactions covered in each chapter within the overall context of the reactions covered in the course.

4 NEW! Problem Solving Strategies have been

added and explicitly highlighted in several chapters, including new strategies for resonance, acid-base equilibria, and multistep synthesis.

5 NEW! Over 100 New Problems include more synthesis problems and problems based on recent literature.

6 NEW! Green Chemistry is emphasized with

presentation of less toxic, environmentally friendly reagents in many situations, such as oxidation of alcohols with bleach rather than with chromium reagents.

7 NEW! Chapter Openers focus on organic

applications, with introductions and images for a more enticing, contemporary presentation.

xxii

8 20 Key Mechanism Boxes highlight the fundamental mechanistic principles that recur throughout the course and are the basis for some of the longer, more complex mechanisms. Each describes the steps of the reaction in detail with a specific example to reinforce the mechanism and a concluding problem to help students absorb these essential reactions.

9 NEW! Explanations and Annotations to

Mechanisms help students better understand how each mechanism works.

Brief Chapter-by-Chapter Changes Global Changes

Every chapter begins with a new chapter-opening photograph showing an interesting, real-world application of the material in that chapter. New Problem-Solving Hints and new Applications have been added to each chapter, and all of the chapters have gone through a careful revision process. All of the structures have been updated to the new IUPAC recommendations for showing stereochemistry. Green curved arrows are used to show the imaginary flow of electrons in resonance forms, in contrast to the red curved arrows used to show the actual flow in reactions.

Chapter 1 ●

The material on structure, bonding, and molecular geometry has been consolidated into one chapter. A revised discussion of resonance includes a ProblemSolving Strategy, a Problem-Solving Hint on the types of arrows used in organic chemistry, and several new problems.

Chapter 2 ●

●

●

●

Several diagrams, applications, problems, and starburst summaries of reactions have been added. The new visual Guide to Organic Reactions is introduced in Chapter 8, and further updated in Chapters 11, 17, 18, 21, and 22.

Chapter 9 Alkynes ●

New examples and a new starburst summary have been added. A new Problem-Solving Hint summarizes oxidative cleavages of alkynes.

Chapter 10 ●

●

Reactions of Alcohols

A newly revised discussion of oxidizing agents emphasizes “green” reactions with sodium hypochlorite and acetic acid, or TEMPO, rather than toxic chromium reagents. A new interim summary compares alcohol oxidations with and without chromium reagents, and a new Problem-Solving Hint discusses ring-size changes and rearrangements. Two new starburst reaction summaries have been added.

Chapter 14 ●

Structure and Synthesis of Alcohols

The material on lithium dialkylcuprates has been expanded into a new section. New Problem-Solving Hints on Grignard reactions and organometallic reactions have also been added. A new starburst reaction summary has been added.

Chapter 11

Alkyl Halides; Nucleophilic Substitution

The sections on E1 and E2 eliminations have been moved to Chapter 7. A new graphic showing the strengths of common nucleophiles has been added, and the summary of nucleophilic substitution conditions has been expanded. Several Problem-Solving Hints have been added on nucleophiles and bases, acid-base strength in the SN1 reaction, and carbocation rearrangements.

This chapter now contains expanded sections on E1 and E2 eliminations. Several Problem-Solving Hints have been added, as well as graphics on the competition between substitutions and eliminations. Several new problems have been added, including two solved problems.

Chapter 8 Reactions of Alkenes

Stereochemistry

This chapter includes a revised summary of types of isomers, with revised figures for clarity. There are new Problem-Solving Hints on stereocenters, Fischer projections, and relative versus absolute configurations.

Chapter 6

●

The Study of Chemical Reactions

The values of bond dissociation enthalpies have been updated to the most recent experimental results throughout the chapter. A revised discussion of Hammond’s postulate includes a figure that has been revised for clarity.

Chapter 5

Chapter 7 Structure and Synthesis of Alkenes; Elimination

Acids and Bases; Functional Groups

The presentation of acids and bases has been moved from the previous Chapter 1 and greatly enhanced to become the main subject in the new Chapter 2. The new material includes sections on inductive, hybridization, resonance, and solvent effects on acidity and basicity; a section and Problem-Solving Strategy on predicting ­acid-base equilibrium positions; new Problem-Solving Hints; new figures; new applications; and 18 new problems.

Chapter 4 ●

Structure and Bonding

Ethers, Epoxides, and Thioethers

New material and a new graphic have been added to clarify the regiochemistry of the opening of substituted epoxides. Several new problems have been added.

xxiii

xxiv

New to This Edition

Chapter 15 Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy ●

Several figures have been revised for clarity, and new applications have been added.

Chapter 16 ●

New to this chapter are a Problem-Solving Hint on drawing energy diagrams for the MOs of cyclic systems, plus new applications and problems. A new starburst reaction summary has also been added.

Chapter 17 ●

●

Amines

A Problem-Solving Hint on pKa of amines has been added, plus new applications and several new problems.

Chapter 20

●

Carboxylic Acids

New problems and applications have been added as well as a starburst reaction summary.

Carboxylic Acid Derivatives

Several new problems and applications have been added, as well as a starburst reaction summary.

Chapter 22 Condensations and Alpha Substitutions of Carbonyl Compounds ●

A new Problem-Solving Hint on ketone and ester carbonyl groups has been added, plus a new starburst reaction summary. Several applications and problems have been added as well.

Chapter 23 ●

●

Amino Acids, Peptides, and Proteins

The material on solid-phase peptide synthesis has been updated to use current techniques, and some of the obsolete, older methods have been deleted.

Chapter 26 ●

Carbohydrates and Nucleic Acids

This chapter has been updated with a new application on glycoproteins. Some of the obsolete older reactions have been dropped.

Chapter 24

Ketones and Aldehydes

The discussion of syntheses of ketones and aldehydes has been revised to emphasize oxidations that use less toxic reagents such as bleach and TEMPO. Several new applications have been added, as well as a starburst reaction summary and several new problems.

Chapter 19 ●

Reactions of Aromatic Compounds

A new Problem-Solving Strategy has been added to explain multistep synthesis using electrophilic aromatic substitutions. The discussion of the Suzuki reaction has been expanded, including its mechanism. New applications, two new starburst reaction summaries, and several problems have also been added.

Chapter 18 ●

Aromatic Compounds

Chapter 21

Synthetic Polymers

The organization of the chapter has been revised to emphasize chain-growth versus step-growth polymers, rather than addition versus condensation polymers. A new section has been added on the recycling of plastics, plus applications on 3D printing and PEX pipes.

Preface To the Student As you begin your study of organic chemistry, you might feel overwhelmed by the number of compounds, names, reactions, and mechanisms that confront you. You might even wonder whether you can learn all this material in a single year. The most important function of a textbook is to organize the material to show that most of organic chemistry consists of a few basic principles and many extensions and applications of these principles. Relatively little memorization is required if you grasp the major concepts and develop flexibility in applying those concepts. Frankly, I have a poor memory, and I hate memorizing lists of information. I don’t remember the specifics of most of the reactions and mechanisms in this book, but I can work them out by remembering a few basic principles, such as “alcohol dehydrations usually go by E1 mechanisms.”

Still, you’ll have to learn some facts and fundamental principles to serve as the working “vocabulary” of each chapter. As a student, I learned this the hard way when I made a D on my second organic chemistry exam. I thought organic would be like general chemistry, where I could memorize a couple of equations and fake my way through the exams. For example, in the ideal gas chapter, I would memorize PV = nRT, and I was good to go. When I tried the same approach in organic, I got a D. We learn by making mistakes, and I learned a lot in organic chemistry.

In writing this book, I’ve tried to point out a small number of important facts and principles that should be learned to prepare for solving problems. For example, of the hundreds of reaction mechanisms shown in this book, about 20 are the fundamental mechanistic steps that combine into the longer, more complicated mechanisms. I’ve highlighted these fundamental mechanisms in Key Mechanism boxes to alert you to their importance. Similarly, the Guide to Organic Reactions appears in six chapters that contain large numbers of new reactions. This guide outlines the kinds of reactions we cover and shows how the reactions just covered fit into the overall organization.

Spectroscopy is another area in which a student might feel pressured to memorize hundreds of facts, such as NMR chemical shifts and infrared vibration frequencies.

I couldn’t do that, so I’ve always gotten by with knowing about a dozen NMR chemical shifts and about a dozen IR vibration frequencies, and knowing how they are affected by other influences. I’ve listed those important infrared frequencies in Table 12-2 and the important NMR chemical shifts in Table 13-3.

Don’t try to memorize your way through this course. It doesn’t work; you have to know what’s going on so you can apply the material. Also, don’t think (like I did) that you can get by without memorizing anything. Read the chapter, listen carefully to the lectures, and work the problems. The problems will tell you whether or not you know the material. If you can do the problems, you should do well on the exams. If you can’t do the problems, you probably won’t be able to do the exams, either. If you keep having to look up an item to do the problems, that item is a good one to learn.

Here are some hints I give my students at the beginning of the course: 1. Read the material in the book before the lecture (expect 13–15 pages per lecture).

Knowing what to expect and what is in the book, you can take fewer notes and spend more time listening and understanding the lecture.

2. After the lecture, review your notes and the book, and do the in-chapter ­problems. Also, read the material for the next lecture.

3. If you are confused about something, visit your instructor during office hours immediately, before you fall behind. Bring your attempted solutions to problems with you to show the instructor where you are having trouble.

xxv

xxvi

Preface

4. To study for an exam, begin by reviewing each chapter and your notes, and ­reviewing any reaction summaries to make sure you can recognize and use those reactions. The “starburst” summaries are most useful for developing syntheses, since you can quickly glance at them and see the most useful conversions for that functional group. Then concentrate on the end-of-chapter problems. In each chapter, the ­Essential Problem-Solving Skills (EPSS) outline reviews the important concepts in the chapter and shows which problems can be used to review each concept. Also use old exams, if available, for practice. Many students find that working in a study group and posing problems for each other is particularly helpful.

Remember the two “golden rules” of organic chemistry.

1. Don’t Get Behind! The course moves too fast, and it’s hard to catch up.

2. Work Lots of Problems. Everyone needs the practice, and the problems show where you need more work.

I am always interested to hear from students using this book. If you have any ­suggestions about how the book might be improved, or if you’ve found an error, please let me know (L. G. Wade, Whitman College, Walla Walla, WA 99362: E-mail wadelg@whitman. edu). I take students’ suggestions seriously, and hundreds of them now appear in this book. For example, Whitman student Brian Lian suggested Figure 21-9, and University of ­Minnesota student (and race-car driver) Jim Coleman gave me the facts on the fuels used at ­Indianapolis.

Good luck with your study of organic chemistry. I’m certain you will enjoy this course, especially if you let yourself relax and develop an interest in how organic compounds influence our lives. My goal in writing this book has been to make the process a little easier: to build the concepts logically on top of each other, so they flow naturally from one to the next. The hints and suggestions for problem solving have helped my students in the past, and I hope some of them will help you to learn and use the material. Even if your memory is worse than mine (highly unlikely), you should be able to do well in organic chemistry. I hope this will be a good learning experience for all of us.

To the Instructor In writing the first edition of this text, my goal was to produce a modern, readable text that uses the most effective techniques of presentation and review. I wanted a book that presents organic chemistry at the level needed for chemistry and biochemistry majors, but one that presents and explains the material in ways that facilitate success for all the many different kinds of students who take the course. Subsequent editions have extended and refined these goals, with substantial rewriting and reorganizing and with many new features. This ninth edition adds several new features to help students organize types of reactions and mechanisms for easier learning and better understanding, as well as for reference.

New to This Edition To help students organize functional group reactions, new Starburst Summaries have been added that provide visual links between synthetically related functional groups.

This new feature is particularly useful when students are developing multistep syntheses, when the visual links help them to see the possible reactions moving forward from a reactant or synthetic intermediate. The new Guides to Organic Reactions will help students to organize mentally the many new reactions they are learning, and where those reactions fit within the overall scheme of the types of reactions we use in organic chemistry. Chapter-opening photographs, with captions that explain how the photograph relates to the chemistry presented in that chapter, have been added to all of the chapters. We have tried to select photos that are remarkable in some way or another and that grab the viewer’s attention.

Preface

All of the features of the earlier editions have been retained in this ninth edition.

In many cases, those that were introduced in earlier editions have been expanded and refined. Many updated applications have been added, including those relating to medicine, green chemistry, biochemistry, and other contemporary areas of interest. Green chemistry is emphasized in many areas, most notably in the use of methods that avoid chromium reagents, which are known to be toxic and carcinogenic. The older, more toxic reagents are mentioned, but they are no longer given as the first choice for a reagent. Mechanisms have been provided for the newest reactions, such as the Suzuki coupling, when they are relevant to the material and studied well enough to be confident they are correct.

Key Features Expanded Coverage of Acids and Bases: After reviewing the basics of bonding, hybridization, and molecular structure in Chapter 1, Chapter 2 is centered around acids and bases and how these concepts apply to organic compounds. The Arrhenius, ­Brønsted-Lowry, and Lewis definitions are introduced and explained. The uses of pKa and pKb are described, followed by a discussion and a Problem-Solving Strategy feature on predicting the position of an acid-base equilibrium reaction. Factors that affect acidity and basicity are explained, including solvent effects, size, electronegativity, inductive effects, hybridization effects, and resonance effects. Lewis acid-base reactions are discussed, with a careful discussion of the correct use of the curved-arrow formalism.

Separation of Substitution and Elimination Reactions: The crucial chapters on substitution and elimination have been revised, with substitutions covered in C ­ hapter 6 and eliminations in Chapter 7. This organization allows students to become more comfortable with the differences between SN1 and SN2 substitutions before the possible reaction pathways are expanded to include eliminations. Chapter 7 presents complete coverage of the competition between substitutions and eliminations, and how one can predict what mechanisms and products are most likely.

Organic Synthesis: Many new synthetic problems have been added, some of them coming from the recent literature. The material on organic synthesis and retrosynthetic analysis has been supplemented, with particular attention to multistep aromatic syntheses.

Nomenclature: We have tried to stay as current as possible with the constantly c­ hanging IUPAC nomenclature, and this edition reflects some of the most recent changes. Beginning with the eighth edition, we have used the 1993 IUPAC positioning of the locants in names (e.g., but-1-ene), while also showing the names using the older positions of the locants (e.g., 1-butene). We have also carefully defined stereochemical terms (such as stereocenter and chiral center) correctly and precisely, and we have endeavored to use the most precise term in each case.

In this edition, we have adopted three of the newest changes in the IUPAC rules: 1. In showing stereochemistry, IUPAC now recommends the “reverse perspective” (closer end is smaller) version of wedged dashed bonds. Wedged solid bonds are still drawn with normal perspective, with their closer end larger.

2. IUPAC now defines hydroxyl as referring only to the radical, not the functional group. The functional group is the hydroxy group. We have changed these terms where needed to conform to this rule.

3. At one time, the IUPAC banished the term ketal. It has now been reinstated as a subclass of acetals, and we have resumed using it.

This ninth edition also includes a new Nomenclature Appendix, which serves as a compact reference to the rules of naming organic compounds. This feature should make it easier for students to name compounds without always having to find the discussion pertaining to that particular functional group.

xxvii

The Keys to Organic Chemistry 340

Structure and Synthesis of Alkenes; Elimination

CHAPTER 7

Among the elimination products, Zaitsev’s rule tells us that the product with the most substituted double bond will predominate.

That is the same product for both the initial carbocation and the rearranged carbocation. However, a substitution product might be the major product. Which one depends on whether the rearrangement is faster than attack by the methanol solvent. If the rearrangement is faster, then we see more rearranged product. This complicated reaction shows why E1 and SN1 reactions of alkyl halides are rarely used for synthesis.

Follow-up question: Show the mechanistic steps that are omitted in the solution to (b) shown above.

Wade & Simek’s ninth edition of Organic Chemistry presents key principles of organic chemistry in the context of ­fundamental reasoning and problem solving. Written to reflect how today’s students use textbooks, this text serves as a primary guide to organic chemistry, as well as a comprehensive study resource when working problems and preparing for exams.

PROBLEM-SOLVING STRATEGY Predicting Substitutions and Eliminations Given a set of reagents and solvents, how can you predict what products will result and which mechanisms will be involved? Should you memorize all this theory about substitutions and eliminations? Students sometimes feel overwhelmed at this point. strong weak Memorizing is not the best way to approach this material because the answers are not absolute Nuc:/base Nuc:/base and too many factors are involved. Besides, the real world with its real reagents and solvents is not as clean as our equations on paper. Most nucleophiles are also basic, and many solvents can SN2 + E2 SN1 + E1 solvate ions or react as nucleophiles or bases.

The first principle you must understand is that you cannot always predict one unique product or one unique mechanism. Often, the best you can do is to eliminate some of the possibilities and make some accurate predictions. Remembering this limitation, here are some general H guidelines: 7-18 Alkene Synthesis by Dehydration of Alcohols 343 1. The strength of the base or nucleophile determines the order of the reaction.

R C X 1° alkyl halide If a strong nucleophile (or base) is present, it will force second-order kinetics, either SN2 or E2.

Like other E1 reactions, an order isofpresent, reactivity that consider first-order reactions, both SN1 H alcohol dehydration If no strongfollows base or nucleophile you should and E1.

Addition silver salts to and the reaction can force some difficult ionizations. reflects carbocation stability: 3° alcohols react faster thanof2° alcohols, 1° alcohols strong weak 2.the Primary halides intermediates usually undergoare thecommon SN2 reaction, are the least reactive. in occasionally the E2 reaction.

Nuc:/baseRearrangements Nuc:/base of Primary first-order reactions, unless the carbocation is resonancealcohol dehydrations. In most cases, Zaitsev’s rule halides applies:rarely The undergo major product is usually stabilized. With good nucleophiles, SN2 substitution is usually observed. With a strong base, the one with the most double bond. no reaction SN2substituted E2 elimination may occasionally be observed.

3. Tertiary halides usually undergo the E2 reaction (strong base) or a mixture of SN1 and E1 (weak base).

SOLVED PROBLEM 77 Tertiary halides cannot undergo the SN2 reaction. A strong base forces second-order kinetR ics, resulting in eliminationof bytert the-butyl E2 mechanism. absence of a strong base, PROBLEM-SOLVING HINTtertiary (a) Propose a mechanism for the sulfuric acid-catalyzed dehydration alcohol. In the R C X 3° alkyl halide halides react by first-order processes, usually a mixture of SN1 and E1. The specific reaction Alcohol dehydrations usually go conditions determine the ratio of substitution to elimination.

S O LU T IO N R through E1 elimination of the The reactions of secondary halides are the most difficult to predict.

The first step is protonation of the hydroxy4.group, which converts it to a good leaving group. protonated strong weak Withalcohol. a weak base and a good With a strong base, either the SN2 or the E2 reaction is possible.

Nuc:/base Nuc:/base CH Reactivity 3°slow.

7 2°Mixtures 7 7 1° of but bothis:are ionizing solvent,CH both SN1 and E1 reactions are possible, 3 3 the H products are common.

Rearrangements are common. + CH3 C O H + H2SO4 CH3 C O + HSO4− E2 SN1 + E1 5. Some nucleophiles and bases favor substitution or elimination.

Protonated primary alcohols H base should readily abstract To promote elimination, the a protonatbut not readily attack a dehydrate elevated temperatures CH3 CH3 elimination. carbon atom. A bulky strong base, such as tert-butoxide with [ -OC(CH 3)3], enhances rearrangement (E1), or the Higher temperatures favor elimination in most cases. To promote substitution, you need The second step is ionization of the protonated alcohol to give aalso carbocation. adjacentspecies carbonthat may a proton R a good nucleophile with limited basicity: a highly polarizable is lose the conjugate a weak base at the same timethat CH3 examples of good nucleophiles base of a strongCH acid. Bromide (Br -) and iodide (I -) areto H R C X 2° alkyl halide water leaves (E2). are weak bases and 3favor substitution. alkyl halides

CH3

O+

C

strong Nuc:/base

H

CH3

CH3

+

C+

H2O

CH3

H

weak Nuc:/base

Abstraction of a proton completes the mechanism.

SN2 + E2 SN1 + E1

H2O

H H

C+

C

CH3

H

CH3

H

CH3 C

+

C

H3O+

CH3

H

(b) Predict the products and propose a mechanism for the acid-catalyzed dehydration of 1-cyclohexylethanol.

PA RT IA L SO LU TI ON:

Protonation of the hydroxy group, followed by loss of water, forms a carbocation.

H H

H

OH C CH3

H

H

+

O

H

C

OSO3H

CH3

H + HSO4–

C

+

CH3 + H2O

1-cyclohexylethanol

carbocation

The carbocation can lose a proton, or it can rearrange to a more stable carbocation.

H H

C

+

H CH3

unrearranged 2° carbocation

˜H

–

+

H C

CH3

rearranged 3° carbocation

Complete this problem by showing how the unrearranged 2° carbocation can lose either of two protons to give two of the following products. Also show how the rearranged 3° carbocation can lose either of two protons to give two of the following products.

xxviii

The resources in this book include Problem-Solving Strategies throughout, plus Partially Solved Problems, Reaction Summaries, new Starburst Summaries, and new Reaction Guides. Through a careful, refined presentation and step-by-step guidance, this ninth edition gives students a contemporary overview of organic chemistry with tools for organizing and understanding reaction mechanisms and synthetic organic chemistry.

Principles, ­Preparation, and Problem Solving 8-17

Olefin Metathesis

415

SUMMARY Electrophilic Additions to Alkenes Methylcyclopentene is an alkene that displays orientation and stereochemistry of addition reactions. New atoms are shown in color. When reactions create chiral products from achiral reactants, racemic mixtures are produced. N/A means “Not Applicable to this reaction.” hydrohalogenation— Markovnikov orientation; stereochemistry N/A; rearrangement can occur Sections 8–2, 8–3

X

hydrobromination with peroxides— anti-Markovnikov orientation; stereochemistry N/A; no rearrangement Section 8–3B

H

CH3

CH3 H

H

H

Br

X

X = Cl, Br, I

H

Br

RO

OR

OH H

H

H+ catalyst H

NaBH4

OH

H

H

X X OH

X

HO

X

OH CH3

OH

NaOH

X = Cl, Br

H CH3

X

hydroboration–oxidation— anti-Markovnikov orientation; syn stereochemistry; no rearrangement Section 8–7

H OH

X CH3

alkoxymercuration– demercuration— Markovnikov orientation; stereochemistry N/A; no rearrangement Section 8–6

H

H

BH3 • THF

catalytic hydrogenation— orientation N/A; syn stereochemistry; no rearrangement Section 8–10

H

OR CH3

NaBH4

H OR Hg(OAc)2

oxymercuration– demercuration— Markovnikov orientation; stereochemistry N/A; no rearrangement Section 8–5

OH CH3

Hg(OAc)2

CH3

H H metal Pt or Pd or Ni

H

H

H

H CH3

H

H

hydration— Markovnikov orientation; stereochemistry N/A; rearrangement can occur Section 8–4

OH CH3

and enantiomer

X

H

H

and enantiomer

and enantiomer

halohydrin formation— Markovnikov orientation; anti stereochemistry; no rearrangement Section 8–9

halogenation— orientation N/A; anti stereochemistry; no rearrangement Section 8–8

Essential Terms

549

GUIDE TO ORGANIC REACTIONS IN

CHAPTER 11

Reactions covered in Chapter 11 are shown in red. Reactions covered in earlier chapters are shown in blue.

Substitution ▶

Nucleophilic

Addition ▶

at C “ O (Nuc. Addn.)

▶

E2 dehydrohalogenation

▶

at sp2 C (Nuc. Arom. Subst.)

▶

at C “ C (conjugate addn.)

▶

tosylate elimination

Ch 9, 10, 18, 22

▶

Electrophilic ▶

Electrophilic

▶

Ch 17, 19

Radical ▶

at sp3 C (alkane halogenation)

▶

at C “ C (Carbene Addn.)

▶

▶

at C “ C (HBr + ROOR)

▶

▶ oxygen functional groups

Ch 11, 18, 19, 20 ▶

E1 dehydrohalogenation

Reduction ▶

hydride reduction

▶

hydrogenation

Ch 8, 10, 11, 17, 18, 19, 20, 21

dehydration of alcohols

Ch 8, 9, 17, 18, 19 ▶ metals

Pericyclic (Cope elimination) ▶

NEW! Visual Guides to Organic Reactions place the reactions covered in each ­chapter within the ­overall context of the reactions ­covered in the course.

Ch 8, 9, 11, 17, 22

Hofmann elimination

Ch 11

Pericyclic ▶

oxidative cleavage

Ch 7

Ch 8

Organometallic

epoxidation

▶

Ch 8, 10, 14

Acidic conditions (E1)

Radical ▶

at sp2 C (Sandmeyer rxn) Ch 19

▶

▶

Ch 4, 6, 16, 17 ▶

at C “ C (Elect. Addn.)

Ch 8

▶

▶

Ch 19

Ch 8, 9, 10

at sp2 C (Elect. Arom. Subst.)

Oxidation

Ch 11 ▶

▶

▶

Ch 7, 9

Ch 22

at C “ O (Nuc. Acyl Subst.)

Ch 10, 11, 20, 21, 22

▶

Oxidation/Reduction

Basic conditions (E2)

▶

Ch 17, 19

▶

▶

at sp3 C (SN1, SN2) Ch 6, 10, 14, 22

▶

Elimination

Nucleophilic

▶

▶

NEW! Starburst Reaction Summaries appear before the end-of-chapter material of “reaction-based” chapters to help students mentally ­organize the reactions and recognize their similarities and differences.

Ch 9, 17, 18, 19

Ch 19

cycloaddition (Diels-Alder) Ch 15

Gilman Ch 10, 17

▶

Suzuki

▶

Heck

▶

▶

Ch 17 Ch 17

Oxidation epoxidation Ch 8, 10, 14

▶

Reduction ▶

hydrogenation Ch 8, 9, 17, 18, 19

xxix

R

O

H

+

Na

R

O − Na+

+

1 2 H2

The Keys to Organic Chemistry Over 80 Mechanism Boxes help students understand how specific reactions occur by zooming in on each individual step in detail.

342

CHAPTER 7

Structure and Synthesis of Alkenes; Elimination

KEY MECHANISM 7-5 Acid-Catalyzed Dehydration of an Alcohol Alcohol dehydrations usually involve E1 elimination of the protonated alcohol.

PROBLEM-SOLVING HINT In acid-catalyzed mechanisms, the first step is often addition of H + , and the last step is often loss of H + .

Step 1: Protonation of the hydroxy group (fast equilibrium).

H H

O

C

C

O

H H

O

S

O

H

H

O+ H HSO4−

C

C

O

Step 2: Ionization to a carbocation (slow; rate limiting).

H +

H

O

C

C

H

H +

+ H2O

C

C

Step 3: Deprotonation to give the alkene (fast).

H

+ H2O

C+

C

+ H3O +

C

C

EXAMPLE: Acid-catalyzed dehydration of butan-2-ol

Step 1: Protonation of the hydroxy group (fast equilibrium).

H

O+ H

CH3

CH

OH CH3

CH

CH2CH3

H2SO4

CH2CH3

Step 2: Ionization to a carbocation (slow; rate limiting).

H

O+ H

CH3

CH

CH2CH3

CH3

+

C

CH2CH3

+

H

O

H

18 Key Mechanism Boxes highlight the fundamental mechanistic principles that recur throughout the course and are the components of many of the longer, more complex mechanisms. Each describes the steps of the reaction in detail with a specific example to reinforce the mechanism and a concluding problem to help students absorb these ­essential reactions.

EW! ­Explanations N and Annotations to Mechanisms help ­students better ­understand how each ­mechanism works.

H Step 3: Deprotonation to give the alkene (fast).

H H

H +

C

C

C

H

H

H

H or

H

C H

xxx

H CH3

+

H

C H

C H

CH3 C

C

H

+

H3O+

H

major product (cis and trans)

H

H C

H2O

H

CH3

H2O

H C H

CH3 C H

C H

minor product

+

H3O+

NEW! Over 100 New Problems include more synthesis problems and problems based on recent research literature.

Principles, Preparation, and Problem Solving www.masteringchemistry.com MasteringChemistry motivates students to practice organic chemistry outside of class and arrive prepared for lecture. The textbook works with MasteringChemistry to guide students toward what they need to know before testing them on the content. This edition continually engages students through pre-lecture, during-, and post-lecture activities that all include real-life applications.

Dynamic Study Modules Help students understand the concepts more quickly!

Now assignable, Dynamic Study Modules enable your students to study on their own and be better prepared with the fundamental concepts needed from general chemistry, as well as the problem solving skills and practice with nomenclature, functional groups, and key mechanisms skills needed to succeed in the organic chemistry course. The ­mobile app is available for iOS and Android ­devices for study on the go, and results can be tracked in the ­MasteringChemistry gradebook.

Spectroscopy Simulations NEW! Six NMR/IR Spectroscopy simulations (a partnership with ACD labs) allow professors and students access to limitless spectral analysis with guided activities that can be used in lab, in the classroom, or after class to study how spectral information correlates with molecular structures.

Activities authored by Mike Huggins, University of West Florida, prompt students to use the spectral simulator to solve analytical problems by drawing the right conclusions from the spectra and combining the NMR and IR data to propose a molecular structure.

xxxi

Resources in Print and Online Supplement

Available in Print?

MasteringChemistry®

Solutions Manual by Jan William Simek

Available Online?

Instructor or Student Supplement

Description

✓

Instructor and Student Supplement

MasteringChemistry New! Organic Chemistry Dynamic Study modules help students efficiently prepare for lecture and exams by reinforcing understanding of general chemistry prerequisites, acid-base chemistry, functional groups, nomenclature, and key mechanisms. At the end of each personalized question set, Dynamic Study Modules provide feedback on whether the answer submitted was correct and give students an explanation of the correct and incorrect answers. The process repeats until the students answer all of the questions correctly and confidently.

(Available at www.­masteringchemistry.com)

Instructor and Student Supplement

This Solutions Manual provides detailed solutions to all in-chapter as well as the endof-chapter exercises in the text. It is now printed in two-color format to highlight details in the solutions and to improve consistency with the text.

✓

Instructor Resources

✓

Instructor Supplement

This website provides an integrated collection of online resources to help instructors make efficient and effective use of their time. It includes all artwork from the text, including figures and tables in PDF format for highresolution printing, as well as four pre-built PowerPoint™ presentations. The first presentation contains the images embedded within PowerPoint slides. The second includes a complete lecture outline that is modifiable by the user. Also available are powerpoints of the parent text “in chapter” sample exercises. It also includes the Test Bank. Access resources through http://www.pearsonhighered.com/.

Testbank

✓

Instructor Supplement

This testbank contains over 3000 multiplechoice, true/false, and matching questions. It is available in print format, in the TestGen program, in Word format, and is included in the item library of MasteringChemistry.

Organic Molecular Kit (Darling)

✓

Instructor and Student Supplement

Darling Models™ contain various pieces used to build atoms, bonds, and molecules. This model kit allows you to build molecules and see the three-dimensional aspects of organic chemistry that can only be imagined in a twodimensional drawing.

Prentice Hall Molecular Model Kit for Organic Chemistry

✓

Instructor and Student Supplement

The Prentice Hall molecular model set allows you to build space-filling and ball-and-stick models of organic molecules. The components are precision-tooled from quality plastics, are virtually indestructible, and come in a sturdy plastic case for easy storage. Provides a useful Instruction Book—with photos, diagrams, and concise discussions of chemical principles.

xxxii

Acknowledgments I am pleased to thank the many talented people who helped with this revision. Certainly the largest contribution has come from Jan William Simek, long-time author of the ­Solutions Manual and now contributing author for this textbook. Jan has provided ­excellent advice and sound judgment through several editions of the book. In this edition, Jan has authored numerous new and ­revised sections, developed over 100 new problems, constructed the starburst reaction summaries, and authored the new Nomenclature Appendix.

Jan and I would also like to thank the many reviewers for their valuable insight and commentary. Although we did not adopt all their suggestions, we adopted most of them; they were helpful and contributed to the quality of the final product.

Ninth Edition Accuracy Reviewers David A. Boyajian Charles Kingsbury Chris Scwhartz Chad Synder

Palomar College University of Nebraska at Lincoln Metropolitan Community College Grace College and Seminary

Ninth Edition Prescriptive Reviewers: Brad Andersh Anonymous Anonymous Ardeshir Azadnia David Boyajian Xuefei Huang Rizalia Klausmeyer Susan Lever Richard Mullins Helena Malinakova Alline Somlai Maria Vogt

Bradley University University of Nebraska-Lincoln West Chester University Michigan State University Palomar College Michigan State University Baylor University University of Missouri-Columbia Xavier University University of Kansas Delta State University Bloomfield College

Additional Reviewers for 9e: Angela Allen Anonymous Anonymous Stefan Bossman Russell Betts Adam Braunschweig Jeffrey Charonnat Joan M. Comar Joseph Cradlebaugh Sean Curtis Markus Etzkorn Ana Fraiman Andy Frazer John Brent Friesen John Hoberg Andrew Holland Jess Jones Raja Mani Joan Mutanyatta Chris Nicholson Oyindasola Oyelaran Ivana Peralta Suzanne Ruder Joshua Ruppel Rekha Srinivasan Eric Trump

Lenoir Community College Emmanuel College Illinois Wesleyan University Kansas State University Broward College Central University of Miami California State University Northridge Georgia State University Jacksonville University University of Arkansas-Ft. Smith University of North Carolina Charlotte Northeastern Illinois University University of Central Florida Dominican University University of Wyoming, Laramie Idaho State University, Pocatello University of South Florida University of Bridgeport Comar, Georgia State University University of West Florida Northeastern University Vincennes University Virginia Commonwealth University University of South Carolina-Upstate Case Western Reserve University Emporia State University

Reviewers of Previous Editions Jung-Mo Ahn David Alonso Merritt B. Andrus Jon Antilla Arthur J. Ashe Bill Baker

University of Texas at Dallas Andrews University Brigham Young University University of South Florida University of Michigan University of South Florida xxxiii

xxxiv

Acknowledgments

Dan Becker John Berger Bob Bly Mary Boyd Hindy Bronstein David Brown Eric Brown Philip Brown Christine Brzezowski Patrick Buick David Cantillo Dee Ann Casteel Amber Charlebois Cai Chengzhi Timothy B. Clark Barry Coddens Jamie Lee Cohen Barbara Colonna Richard Conley Robert Crow Maria de GracaVicente James Fletcher Chris Gorman Geneive Henry William Jenks Przemyslaw Maslak Kristen Meisenheimer Guillermo Moyna Rabi Musah Stephen A. Miller Hasan Palandoken Keith Osbourne Pascoe Anthony J. Pearson Allan Pinhas Owen Priest Stanley Raucher Suzanne Ruder K.C. Russell Alline Somlai Joseph B. Wachter David Son Solomon Weldegirma

Loyola University Montclair State University University of South Carolina Loyola University, Chicago Fordham College at Lincoln Center St. John’s University Loyola University, Lake Shore North Carolina State University University of Alberta Florida Atlantic University Hillsborough Community College Bucknell University William Paterson University University of Houston Western Washington University Northwestern University Pace University University of Miami Middlesex County College St. Louis College of Pharmacy Louisiana State University Creighton University North Carolina State University Susquehanna University Iowa State University Pennsylvania State University Cal Polytechnic at San Luis Obispo University of the Sciences in Philadelphia University at Albany University of Florida California Polytechnic State University Georgia State University Case Western Reserve University of Cincinnati Northwestern University University ofWashington Virginia Commonwealth University Northern Kentucky University Delta State University Michigan State University Southern Methodist University University of South Florida

Finally, we want to thank the people at Pearson, whose dedication and commitment contributed to the completion of this project. Particular thanks are due to Developmental Editor David Chelton, who made thousands of useful suggestions throughout the writing and revision process, and who helped to shape this new edition. Special thanks are also due to Editorin-Chief Jeanne Zalesky, who guided the project from start to finish and made many useful comments and suggestions that guided the direction of the revision. Director of Development Jennifer Hart and Program Manager Lisa Pierce kept the project moving and ensured the needed resources were made available. Project Managers Elisa Mandelbaum and Heidi Aguiar, and Text and Image Research Lead Maya Gomez kept the production process organized, on track, and on schedule. It has been a pleasure working with all these thoroughly professional and competent people.

We have enjoyed working on this new edition, and we hope that it is a scientific and pedagogical improvement over the eighth edition. We’ve tried to make this book as error-free as possible, but some errors may have slipped by. If you find errors, or have suggestions about how the book might be improved, please send those errors and suggestions to me at my e-mail address: wadelg@whitman.edu. Errors can be fixed quickly in the next printing. Please send any errors you find in the Solutions Manual, or suggestions for improvements, to Jan Simek at his e-mail address: jsimek@calpoly.edu.

We’ve already started a file of possible changes and improvements for the next edition, and we hope that many of the current users will contribute suggestions to this file. We hope this book makes the instructor’s job easier and helps more students to succeed. That’s the most important reason that we continue to work at improving it.

L. G. Wade, Jr. Walla Walla, Washington Jan William Simek San Luis Obispo, California

Another random document with no related content on Scribd:

DANCE ON STILTS AT THE GIRLS’ UNYAGO, NIUCHI

Newala, too, suffers from the distance of its water-supply—at least the Newala of to-day does; there was once another Newala in a lovely valley at the foot of the plateau. I visited it and found scarcely a trace of houses, only a Christian cemetery, with the graves of several missionaries and their converts, remaining as a monument of its former glories. But the surroundings are wonderfully beautiful. A thick grove of splendid mango-trees closes in the weather-worn crosses and headstones; behind them, combining the useful and the agreeable, is a whole plantation of lemon-trees covered with ripe fruit; not the small African kind, but a much larger and also juicier imported variety, which drops into the hands of the passing traveller, without calling for any exertion on his part. Old Newala is now under the jurisdiction of the native pastor, Daudi, at Chingulungulu, who, as I am on very friendly terms with him, allows me, as a matter of course, the use of this lemon-grove during my stay at Newala.

FEET MUTILATED BY THE RAVAGES OF THE “JIGGER” (Sarcopsylla penetrans)

The water-supply of New Newala is in the bottom of the valley, some 1,600 feet lower down. The way is not only long and fatiguing, but the water, when we get it, is thoroughly bad. We are suffering not only from this, but from the fact that the arrangements at Newala are nothing short of luxurious. We have a separate kitchen—a hut built against the boma palisade on the right of the baraza, the interior of which is not visible from our usual position. Our two cooks were not long in finding this out, and they consequently do—or rather neglect to do—what they please. In any case they do not seem to be very particular about the boiling of our drinking-water—at least I can attribute to no other cause certain attacks of a dysenteric nature, from which both Knudsen and I have suffered for some time. If a man like Omari has to be left unwatched for a moment, he is capable of anything. Besides this complaint, we are inconvenienced by the state of our nails, which have become as hard as glass, and crack on the slightest provocation, and I have the additional infliction of pimples all over me. As if all this were not enough, we have also, for the last week been waging war against the jigger, who has found his Eldorado in the hot sand of the Makonde plateau. Our men are seen all day long—whenever their chronic colds and the dysentery likewise raging among them permit—occupied in removing this scourge of Africa from their feet and trying to prevent the disastrous consequences of its presence. It is quite common to see natives of this place with one or two toes missing; many have lost all their toes,

or even the whole front part of the foot, so that a well-formed leg ends in a shapeless stump. These ravages are caused by the female of Sarcopsylla penetrans, which bores its way under the skin and there develops an egg-sac the size of a pea. In all books on the subject, it is stated that one’s attention is called to the presence of this parasite by an intolerable itching. This agrees very well with my experience, so far as the softer parts of the sole, the spaces between and under the toes, and the side of the foot are concerned, but if the creature penetrates through the harder parts of the heel or ball of the foot, it may escape even the most careful search till it has reached maturity.

Then there is no time to be lost, if the horrible ulceration, of which we see cases by the dozen every day, is to be prevented. It is much easier, by the way, to discover the insect on the white skin of a European than on that of a native, on which the dark speck scarcely shows. The four or five jiggers which, in spite of the fact that I constantly wore high laced boots, chose my feet to settle in, were taken out for me by the all-accomplished Knudsen, after which I thought it advisable to wash out the cavities with corrosive sublimate. The natives have a different sort of disinfectant—they fill the hole with scraped roots. In a tiny Makua village on the slope of the plateau south of Newala, we saw an old woman who had filled all the spaces under her toe-nails with powdered roots by way of prophylactic treatment. What will be the result, if any, who can say?

The rest of the many trifling ills which trouble our existence are really more comic than serious. In the absence of anything else to smoke, Knudsen and I at last opened a box of cigars procured from the Indian store-keeper at Lindi, and tried them, with the most distressing results. Whether they contain opium or some other narcotic, neither of us can say, but after the tenth puff we were both “off,” three-quarters stupefied and unspeakably wretched. Slowly we recovered—and what happened next? Half-an-hour later we were once more smoking these poisonous concoctions—so insatiable is the craving for tobacco in the tropics.

Even my present attacks of fever scarcely deserve to be taken seriously. I have had no less than three here at Newala, all of which have run their course in an incredibly short time. In the early afternoon, I am busy with my old natives, asking questions and making notes. The strong midday coffee has stimulated my spirits to

an extraordinary degree, the brain is active and vigorous, and work progresses rapidly, while a pleasant warmth pervades the whole body. Suddenly this gives place to a violent chill, forcing me to put on my overcoat, though it is only half-past three and the afternoon sun is at its hottest. Now the brain no longer works with such acuteness and logical precision; more especially does it fail me in trying to establish the syntax of the difficult Makua language on which I have ventured, as if I had not enough to do without it. Under the circumstances it seems advisable to take my temperature, and I do so, to save trouble, without leaving my seat, and while going on with my work. On examination, I find it to be 101·48°. My tutors are abruptly dismissed and my bed set up in the baraza; a few minutes later I am in it and treating myself internally with hot water and lemon-juice.

Three hours later, the thermometer marks nearly 104°, and I make them carry me back into the tent, bed and all, as I am now perspiring heavily, and exposure to the cold wind just beginning to blow might mean a fatal chill. I lie still for a little while, and then find, to my great relief, that the temperature is not rising, but rather falling. This is about 7.30 p.m. At 8 p.m. I find, to my unbounded astonishment, that it has fallen below 98·6°, and I feel perfectly well. I read for an hour or two, and could very well enjoy a smoke, if I had the wherewithal—Indian cigars being out of the question.

Having no medical training, I am at a loss to account for this state of things. It is impossible that these transitory attacks of high fever should be malarial; it seems more probable that they are due to a kind of sunstroke. On consulting my note-book, I become more and more inclined to think this is the case, for these attacks regularly follow extreme fatigue and long exposure to strong sunshine. They at least have the advantage of being only short interruptions to my work, as on the following morning I am always quite fresh and fit.

My treasure of a cook is suffering from an enormous hydrocele which makes it difficult for him to get up, and Moritz is obliged to keep in the dark on account of his inflamed eyes. Knudsen’s cook, a raw boy from somewhere in the bush, knows still less of cooking than Omari; consequently Nils Knudsen himself has been promoted to the vacant post. Finding that we had come to the end of our supplies, he began by sending to Chingulungulu for the four sucking-pigs which we had

bought from Matola and temporarily left in his charge; and when they came up, neatly packed in a large crate, he callously slaughtered the biggest of them. The first joint we were thoughtless enough to entrust for roasting to Knudsen’s mshenzi cook, and it was consequently uneatable; but we made the rest of the animal into a jelly which we ate with great relish after weeks of underfeeding, consuming incredible helpings of it at both midday and evening meals. The only drawback is a certain want of variety in the tinned vegetables. Dr. Jäger, to whom the Geographical Commission entrusted the provisioning of the expeditions—mine as well as his own—because he had more time on his hands than the rest of us, seems to have laid in a huge stock of Teltow turnips,[46] an article of food which is all very well for occasional use, but which quickly palls when set before one every day; and we seem to have no other tins left. There is no help for it—we must put up with the turnips; but I am certain that, once I am home again, I shall not touch them for ten years to come.

Amid all these minor evils, which, after all, go to make up the genuine flavour of Africa, there is at least one cheering touch: Knudsen has, with the dexterity of a skilled mechanic, repaired my 9 × 12 cm. camera, at least so far that I can use it with a little care.

How, in the absence of finger-nails, he was able to accomplish such a ticklish piece of work, having no tool but a clumsy screw-driver for taking to pieces and putting together again the complicated mechanism of the instantaneous shutter, is still a mystery to me; but he did it successfully. The loss of his finger-nails shows him in a light contrasting curiously enough with the intelligence evinced by the above operation; though, after all, it is scarcely surprising after his ten years’ residence in the bush. One day, at Lindi, he had occasion to wash a dog, which must have been in need of very thorough cleansing, for the bottle handed to our friend for the purpose had an extremely strong smell. Having performed his task in the most conscientious manner, he perceived with some surprise that the dog did not appear much the better for it, and was further surprised by finding his own nails ulcerating away in the course of the next few days. “How was I to know that carbolic acid has to be diluted?” he mutters indignantly, from time to time, with a troubled gaze at his mutilated finger-tips.

Since we came to Newala we have been making excursions in all directions through the surrounding country, in accordance with old habit, and also because the akida Sefu did not get together the tribal elders from whom I wanted information so speedily as he had promised. There is, however, no harm done, as, even if seen only from the outside, the country and people are interesting enough.

The Makonde plateau is like a large rectangular table rounded off at the corners. Measured from the Indian Ocean to Newala, it is about seventy-five miles long, and between the Rovuma and the Lukuledi it averages fifty miles in breadth, so that its superficial area is about two-thirds of that of the kingdom of Saxony. The surface, however, is not level, but uniformly inclined from its south-western edge to the ocean. From the upper edge, on which Newala lies, the eye ranges for many miles east and north-east, without encountering any obstacle, over the Makonde bush. It is a green sea, from which here and there thick clouds of smoke rise, to show that it, too, is inhabited by men who carry on their tillage like so many other primitive peoples, by cutting down and burning the bush, and manuring with the ashes. Even in the radiant light of a tropical day such a fire is a grand sight.

Much less effective is the impression produced just now by the great western plain as seen from the edge of the plateau. As often as time permits, I stroll along this edge, sometimes in one direction, sometimes in another, in the hope of finding the air clear enough to let me enjoy the view; but I have always been disappointed.

Wherever one looks, clouds of smoke rise from the burning bush, and the air is full of smoke and vapour. It is a pity, for under more favourable circumstances the panorama of the whole country up to the distant Majeje hills must be truly magnificent. It is of little use taking photographs now, and an outline sketch gives a very poor idea of the scenery. In one of these excursions I went out of my way to make a personal attempt on the Makonde bush. The present edge of the plateau is the result of a far-reaching process of destruction through erosion and denudation. The Makonde strata are everywhere cut into by ravines, which, though short, are hundreds of yards in depth. In consequence of the loose stratification of these beds, not only are the walls of these ravines nearly vertical, but their upper end is closed by an equally steep escarpment, so that the

western edge of the Makonde plateau is hemmed in by a series of deep, basin-like valleys. In order to get from one side of such a ravine to the other, I cut my way through the bush with a dozen of my men.

It was a very open part, with more grass than scrub, but even so the short stretch of less than two hundred yards was very hard work; at the end of it the men’s calicoes were in rags and they themselves bleeding from hundreds of scratches, while even our strong khaki suits had not escaped scatheless.

NATIVE PATH THROUGH THE MAKONDE BUSH, NEAR MAHUTA

I see increasing reason to believe that the view formed some time back as to the origin of the Makonde bush is the correct one. I have no doubt that it is not a natural product, but the result of human occupation. Those parts of the high country where man—as a very slight amount of practice enables the eye to perceive at once—has not yet penetrated with axe and hoe, are still occupied by a splendid timber forest quite able to sustain a comparison with our mixed forests in Germany. But wherever man has once built his hut or tilled his field, this horrible bush springs up. Every phase of this process

may be seen in the course of a couple of hours’ walk along the main road. From the bush to right or left, one hears the sound of the axe— not from one spot only, but from several directions at once. A few steps further on, we can see what is taking place. The brush has been cut down and piled up in heaps to the height of a yard or more, between which the trunks of the large trees stand up like the last pillars of a magnificent ruined building. These, too, present a melancholy spectacle: the destructive Makonde have ringed them— cut a broad strip of bark all round to ensure their dying off—and also piled up pyramids of brush round them. Father and son, mother and son-in-law, are chopping away perseveringly in the background—too busy, almost, to look round at the white stranger, who usually excites so much interest. If you pass by the same place a week later, the piles of brushwood have disappeared and a thick layer of ashes has taken the place of the green forest. The large trees stretch their smouldering trunks and branches in dumb accusation to heaven—if they have not already fallen and been more or less reduced to ashes, perhaps only showing as a white stripe on the dark ground.

This work of destruction is carried out by the Makonde alike on the virgin forest and on the bush which has sprung up on sites already cultivated and deserted. In the second case they are saved the trouble of burning the large trees, these being entirely absent in the secondary bush.

After burning this piece of forest ground and loosening it with the hoe, the native sows his corn and plants his vegetables. All over the country, he goes in for bed-culture, which requires, and, in fact, receives, the most careful attention. Weeds are nowhere tolerated in the south of German East Africa. The crops may fail on the plains, where droughts are frequent, but never on the plateau with its abundant rains and heavy dews. Its fortunate inhabitants even have the satisfaction of seeing the proud Wayao and Wamakua working for them as labourers, driven by hunger to serve where they were accustomed to rule.

But the light, sandy soil is soon exhausted, and would yield no harvest the second year if cultivated twice running. This fact has been familiar to the native for ages; consequently he provides in time, and, while his crop is growing, prepares the next plot with axe and firebrand. Next year he plants this with his various crops and

lets the first piece lie fallow. For a short time it remains waste and desolate; then nature steps in to repair the destruction wrought by man; a thousand new growths spring out of the exhausted soil, and even the old stumps put forth fresh shoots. Next year the new growth is up to one’s knees, and in a few years more it is that terrible, impenetrable bush, which maintains its position till the black occupier of the land has made the round of all the available sites and come back to his starting point.

The Makonde are, body and soul, so to speak, one with this bush.

According to my Yao informants, indeed, their name means nothing else but “bush people.” Their own tradition says that they have been settled up here for a very long time, but to my surprise they laid great stress on an original immigration. Their old homes were in the south-east, near Mikindani and the mouth of the Rovuma, whence their peaceful forefathers were driven by the continual raids of the Sakalavas from Madagascar and the warlike Shirazis[47] of the coast, to take refuge on the almost inaccessible plateau. I have studied African ethnology for twenty years, but the fact that changes of population in this apparently quiet and peaceable corner of the earth could have been occasioned by outside enterprises taking place on the high seas, was completely new to me. It is, no doubt, however, correct.

The charming tribal legend of the Makonde—besides informing us of other interesting matters—explains why they have to live in the thickest of the bush and a long way from the edge of the plateau, instead of making their permanent homes beside the purling brooks and springs of the low country.

“The place where the tribe originated is Mahuta, on the southern side of the plateau towards the Rovuma, where of old time there was nothing but thick bush. Out of this bush came a man who never washed himself or shaved his head, and who ate and drank but little.

He went out and made a human figure from the wood of a tree growing in the open country, which he took home to his abode in the bush and there set it upright. In the night this image came to life and was a woman. The man and woman went down together to the Rovuma to wash themselves. Here the woman gave birth to a stillborn child. They left that place and passed over the high land into the valley of the Mbemkuru, where the woman had another child, which

was also born dead. Then they returned to the high bush country of Mahuta, where the third child was born, which lived and grew up. In course of time, the couple had many more children, and called themselves Wamatanda. These were the ancestral stock of the Makonde, also called Wamakonde,[48] i.e., aborigines. Their forefather, the man from the bush, gave his children the command to bury their dead upright, in memory of the mother of their race who was cut out of wood and awoke to life when standing upright. He also warned them against settling in the valleys and near large streams, for sickness and death dwelt there. They were to make it a rule to have their huts at least an hour’s walk from the nearest wateringplace; then their children would thrive and escape illness.”

The explanation of the name Makonde given by my informants is somewhat different from that contained in the above legend, which I extract from a little book (small, but packed with information), by Pater Adams, entitled Lindi und sein Hinterland. Otherwise, my results agree exactly with the statements of the legend. Washing?

Hapana—there is no such thing. Why should they do so? As it is, the supply of water scarcely suffices for cooking and drinking; other people do not wash, so why should the Makonde distinguish himself by such needless eccentricity? As for shaving the head, the short, woolly crop scarcely needs it,[49] so the second ancestral precept is likewise easy enough to follow. Beyond this, however, there is nothing ridiculous in the ancestor’s advice. I have obtained from various local artists a fairly large number of figures carved in wood, ranging from fifteen to twenty-three inches in height, and representing women belonging to the great group of the Mavia, Makonde, and Matambwe tribes. The carving is remarkably well done and renders the female type with great accuracy, especially the keloid ornamentation, to be described later on. As to the object and meaning of their works the sculptors either could or (more probably) would tell me nothing, and I was forced to content myself with the scanty information vouchsafed by one man, who said that the figures were merely intended to represent the nembo—the artificial deformations of pelele, ear-discs, and keloids. The legend recorded

by Pater Adams places these figures in a new light. They must surely be more than mere dolls; and we may even venture to assume that they are—though the majority of present-day Makonde are probably unaware of the fact—representations of the tribal ancestress.

The references in the legend to the descent from Mahuta to the Rovuma, and to a journey across the highlands into the Mbekuru valley, undoubtedly indicate the previous history of the tribe, the travels of the ancestral pair typifying the migrations of their descendants. The descent to the neighbouring Rovuma valley, with its extraordinary fertility and great abundance of game, is intelligible at a glance—but the crossing of the Lukuledi depression, the ascent to the Rondo Plateau and the descent to the Mbemkuru, also lie within the bounds of probability, for all these districts have exactly the same character as the extreme south. Now, however, comes a point of especial interest for our bacteriological age. The primitive Makonde did not enjoy their lives in the marshy river-valleys.

Disease raged among them, and many died. It was only after they had returned to their original home near Mahuta, that the health conditions of these people improved. We are very apt to think of the African as a stupid person whose ignorance of nature is only equalled by his fear of it, and who looks on all mishaps as caused by evil spirits and malignant natural powers. It is much more correct to assume in this case that the people very early learnt to distinguish districts infested with malaria from those where it is absent.

This knowledge is crystallized in the ancestral warning against settling in the valleys and near the great waters, the dwelling-places of disease and death. At the same time, for security against the hostile Mavia south of the Rovuma, it was enacted that every settlement must be not less than a certain distance from the southern edge of the plateau. Such in fact is their mode of life at the present day. It is not such a bad one, and certainly they are both safer and more comfortable than the Makua, the recent intruders from the south, who have made USUAL METHOD OF good their footing on the western edge of the CLOSING HUT-DOOR plateau, extending over a fairly wide belt of country. Neither Makua nor Makonde show in their dwellings anything of the size and comeliness of the Yao houses in the plain, especially at Masasi, Chingulungulu and Zuza’s. Jumbe Chauro, a Makonde hamlet not far from Newala, on the road to Mahuta, is the

most important settlement of the tribe I have yet seen, and has fairly spacious huts. But how slovenly is their construction compared with the palatial residences of the elephant-hunters living in the plain.

The roofs are still more untidy than in the general run of huts during the dry season, the walls show here and there the scanty beginnings or the lamentable remains of the mud plastering, and the interior is a veritable dog-kennel; dirt, dust and disorder everywhere. A few huts only show any attempt at division into rooms, and this consists merely of very roughly-made bamboo partitions. In one point alone have I noticed any indication of progress—in the method of fastening the door. Houses all over the south are secured in a simple but ingenious manner. The door consists of a set of stout pieces of wood or bamboo, tied with bark-string to two cross-pieces, and moving in two grooves round one of the door-posts, so as to open inwards. If the owner wishes to leave home, he takes two logs as thick as a man’s upper arm and about a yard long. One of these is placed obliquely against the middle of the door from the inside, so as to form an angle of from 60° to 75° with the ground. He then places the second piece horizontally across the first, pressing it downward with all his might.

It is kept in place by two strong posts planted in the ground a few inches inside the door. This fastening is absolutely safe, but of course cannot be applied to both doors at once, otherwise how could the owner leave or enter his house? I have not yet succeeded in finding out how the back door is fastened.

MAKONDE LOCK AND KEY AT JUMBE CHAURO

This is the general way of closing a house. The Makonde at Jumbe Chauro, however, have a much more complicated, solid and original one. Here, too, the door is as already described, except that there is only one post on the inside, standing by itself about six inches from one side of the doorway. Opposite this post is a hole in the wall just large enough to admit a man’s arm. The door is closed inside by a large wooden bolt passing through a hole in this post and pressing with its free end against the door. The other end has three holes into which fit three pegs running in vertical grooves inside the post. The door is opened with a wooden key about a foot long, somewhat curved and sloped off at the butt; the other end has three pegs corresponding to the holes, in the bolt, so that, when it is thrust through the hole in the wall and inserted into the rectangular opening in the post, the pegs can be lifted and the bolt drawn out.[50]

MODE OF INSERTING THE KEY

With no small pride first one householder and then a second showed me on the spot the action of this greatest invention of the Makonde Highlands. To both with an admiring exclamation of “Vizuri sana!” (“Very fine!”). I expressed the wish to take back these marvels with me to Ulaya, to show the Wazungu what clever fellows the Makonde are. Scarcely five minutes after my return to camp at Newala, the two men came up sweating under the weight of two heavy logs which they laid down at my feet, handing over at the same time the keys of the fallen fortress. Arguing, logically enough, that if the key was wanted, the lock would be wanted with it, they had taken their axes and chopped down the posts—as it never occurred to them to dig them out of the ground and so bring them intact. Thus I have

two badly damaged specimens, and the owners, instead of praise, come in for a blowing-up.

The Makua huts in the environs of Newala are especially miserable; their more than slovenly construction reminds one of the temporary erections of the Makua at Hatia’s, though the people here have not been concerned in a war. It must therefore be due to congenital idleness, or else to the absence of a powerful chief. Even the baraza at Mlipa’s, a short hour’s walk south-east of Newala, shares in this general neglect. While public buildings in this country are usually looked after more or less carefully, this is in evident danger of being blown over by the first strong easterly gale. The only attractive object in this whole district is the grave of the late chief Mlipa. I visited it in the morning, while the sun was still trying with partial success to break through the rolling mists, and the circular grove of tall euphorbias, which, with a broken pot, is all that marks the old king’s resting-place, impressed one with a touch of pathos.

Even my very materially-minded carriers seemed to feel something of the sort, for instead of their usual ribald songs, they chanted solemnly, as we marched on through the dense green of the Makonde bush:—