RSM12-P-IV -T(M)-CH(S) - 4
-> CH2=CH—CH2—C = CH 2 (Vinylic carbocation)
CH2=CH-CH2—C£CTA+ HBR-
:Br CH2—CH—CH2—C—CH2 I
2° - carbocation being relatively far more stable than the vinylic carbocation, addition occurs at ethvlenic linkage rather than on acetylenic linkage. b) h2C-—-CH2 + RNH 2 - — > CH2—CH2OH R—ILH (3-amino alcohol The product p-amino alcohol is less nucleophilic because of stabilisation by intramolecular hydrogen bonding between the lone pair of electron on nitrogen and partially acidic hydrogen of the alcoholic group. H s+ H
^J
5
-
>
2
r / ^ c ^N h 22 R' c) In this case, the mechanism involves the participation of the carboxylate group as given below
Step: 1
Inversion H ;H
+ AgBr
Br. Ag+
An a-lactone (highly strained)
Step 2: COO" -H
CH3
+
H
CH3
OH
The net result of two inversions is an overall retention of configuration. The phenemenon is called neighbouring group participation. 8.
a) The most probable mechanism appears to be elimination addition one involving benzyne intermediate as shown below.
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