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JEE MainChemistryAldehydes and Ketones

Consider the following carbonyl compounds: (I) p -Nitrobenzaldehyde (II) Benzaldehyde (III) p -Methoxybenzaldehyde (IV) Acetophenone The correct decreasing order of their reactivity towards nucleophilic addition of HCN is:

Options

  1. A(IV) > (III) > (II) > (I)
  2. B(I) > (II) > (III) > (IV)
  3. C(I) > (III) > (II) > (IV)
  4. D(II) > (I) > (III) > (IV)

Correct answer

B. (I) > (II) > (III) > (IV)

Step-by-step solution

Reactivity of carbonyl compounds towards nucleophilic addition depends on the magnitude of the positive charge on the carbonyl carbon and steric hindrance. Acetophenone (IV) is a ketone, which has an extra methyl group compared to the aldehydes. This provides more steric hindrance and a +I effect, making it the least reactive. Among the aldehydes, electron-withdrawing groups increase the positive charge on the carbonyl carbon, enhancing reactivity, while electron-donating groups decrease it. In p -nitrobenzaldehyde

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