Nucleophilic Acyl Substitution in the Basic Hydrolysis of an Ester

Nucleophilic Acyl Substitution in the Basic Hydrolysis of an Ester 

Step I Hydroxide ion (strong nucleophile) adds to the carbonyl group, forming a tetrahedral intermediate. 

Step 2 An alkoxide ion leaves, regenerating the C=0 double bond. 

Step 3 A fast, exothermic proton transfer drives the reaction to completion. 

Nucleophilic acyl substitution also takes place in acid. Under acidic conditions, no strong nucleophile is present to attack the carbonyl group. The carbonyl group must become protonated, activating it toward nucleophilic acyl substitution. Attack by a weak nucleophile gives a tetrahedral intermediate. In most cases, the leaving group becomes protonated before it leaves, so it leaves as a neutral molecule. We now cover the most useful example of an acid-catalyzed nucleophilic acyl substitution the Fischer esterification. 

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Nucleophilic Acyl Substitution 960 Mechanism 20-1 Nucleophilic Acyl Substitution in the Basic Hydrolysis of an Ester 960... 

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