JEE Main Chemistry question

The increasing order of the rate of HCN addition to compounds A–D is: I. HCHO; II. CH₃COCH₃; III. PhCOCH₃; IV. PhCOPh. The correct order is

(A)A < B < C < D
(B)D < B < C < A
(C)D < C < B < ACorrect
(D)C < D < B < A

Answer: (C)

Solution

Nucleophilic addition of HCN to a carbonyl is favoured by a less hindered, more electrophilic carbonyl carbon. HCHO (I, smallest, most electrophilic) reacts fastest, followed by the dialkyl ketone acetone (II), then the aryl–alkyl ketone acetophenone (III, phenyl donates electron

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Question ID VK-149207