Question 2 in nucleophilic acyl substitution protonation of...

'Question 2 In nucleophilic acyl substitution, protonation of the carbonyl is followed immediately by loss of the leaving group_ loss of the leaving group is followed by rearrangement of the carbocation: addition to the carbonyl by a nucleophile is followed by loss of the leaving group. ester hydrolysis is followed by deprotonation: an SN2 reaction occurs_'

Amides undergo hydrolysis to yield carboxylic acid plus amine on heating in either aqueous acid or aqueous base. The conditions required for amide hydrolysis are more severe than those required for the hydrolysis of esters, anhydrides or acid chlorides, but the mechanism is similar (nucleophilic acyl substitution). Nucleophilic acyl substitutions involve a tetrahedral intermediate, hence these are quite different from alkyl substitution $\left(\mathrm{RCH}_{2} \mathrm{Br} \underset{\mathrm{NaCN}}{\rightarrow} \mathrm{RCH}_{2} \mathrm{CN}\right)$ which involves a pentavalent intermediate or transition state. One of the important reactions of esters is their reaction with two equivalent of a Grignard reagent to give tertiary alcohols. The mechanism involved during the hydrolysis of acid derivatives is (a) elimination-addition (b) addition-elimination (c) nucleophilic addition-elimination (d) electrophilic addition-elimination

Advanced Problems in Organic Chemistry for Competitive Examinations

Organic Reaction Mechanisms and Reagents

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