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ConsidertheelectrophilicadditionofH-Brtobutene:ThealkeneabstractsaprotonfromtheHBr,andacarbocationandbromideionaregeneratedAlkenes undergoelectrophilicadditionreactions.Thereactionoccursintwosteps,protonationandbromideaddition,andinvolvesacarbocationintermediate.Mostof thesereactonsareelectrophilicadditions,ortheadditionofelectrophilesacrossthedoublebond9ElectrophilicAdditionReactionsofAlkenesandAlkynes INTRODUCTIONChapterismostlyaboutalkenereactionsFormingstructuralisomersbyadditionreactions(onpinChemistry3)AdditionofThereactionisoften doneinamixoforganicsolventandwaterusingN-bromosuccinimide(NBS)astheelectrophilicbrominesourceHydrogenchlorideandhydrogenbromidereact withalkenestogiveadditionproductsInearlyAcarefulstudyofthisandsimilarreactionsbytheBritishchemistChristopherIngoldandothersinthesledtothe generallyacceptedmechanismshowninFigureforanReactions,alkenesAdditionofhydrogen(reduction)AdditionofhalogensAdditionofhydrogenhalidesInionic electrophilicadditiontoanalkene,thealkynes:electrophilic.Electrophilicaddition.additionpericyclicreactions.Mechanism:ElectrophilicAddition.Electrophilic additiontoElectrophilicAdditiontoAlkenesAdditionofHydrogenHalides.Thatis,howonecantransformalkenesintootherfunctionalgroups.Answersto workedexamplesThereactionbeginswithanattackonthehydrogenoftheelectrophileHBrbytheelectronsofthenucleophilicπbondAhydrogenatomjoinsto oneofthecarbonatomsoriginallyDownloadPDFTestYourselfwritethemechanismforthereactionofaproticacid,HX,withanalkeneWhathappens?and Thebromideionquicklyattacksthecationiccenterandyieldsthefinalproductexplaintheterm“electrophilicadditionreaction,”usingthereactionofaproticacid, HX,withanalkeneasanexampleThefirststepisslowerthanthesecondstepThisnewcarbocationlosesaprotoninsteptoformamixtureof2,4,4trimethylpenteneand2,4,4-trimethylpenteneMechanismoftheelectrophilicadditionofHBrtomethylpropeneDMSO,H2ONOO+BrBrOHNOO+H Additiontosymmetricalalkenes.sketchareactionenergydiagramfortheelectrophilicadditionofanacid,HX,toanalkeneELECTROPHILICADDITIONS OFALKENESASTHECOUNTERPARTOFELIMINATIONSInanelectrophilicaddition•AdditionReactions•ElectrophilicAdditionofH-XorX2to Alkenes•AdditionofH-XandX2toAlkynes•AlkenestoAlcoholsbyElectrophilicAddition•AlkenestoAlcoholsbyHydroboration•AdditionofH2toAlkenes andAlkynesPreview(Tobeadded)AdditionReactionsElectrophilicadditionisprobablythemostcommonreactionofalkenesAllalkenesundergoaddition reactionswiththehydrogenhalidesFigureEnergydiagramforthetwo-stepelectrophilicadditionofHBrtomethylpropeneREACTIONSOFALKENES INTRODUCTIONAlkeneshaveaplanarstructureand,asyouwillremember,thesocalled'doublebond'infactconsistsofasigma-bond(end-onoverlapof Sphybridatomicorbitals)andapi-bond(sidewaysoverlapof2patomicorbitals)Thecarbocationisanelectrophileandattacksasecondmolecule ofmethylpropeneinstep2,forminganewcarbon–carbonbondandgeneratingaC8carbocation.