Arrange the following compounds in increasing order of their reactivity towards HCN.

Choose the correct answer from the options given below:

(C), (D), (B), (A)

The correct answer is Option (2) → (C), (D), (B), (A)

HCN adds to carbonyl compounds via nucleophilic addition.

Reactivity depends on: • Steric hindrance • +I effect of alkyl groups

More bulky alkyl groups → Less reactivity

Aldehydes react faster than ketones because: • Less steric hindrance • Less electron donation

Reactivity order: Highly bulky ketone < Moderately bulky ketone < Simple ketone < Aldehyde

Identify the compounds

• (A) CH₃CHO (acetaldehyde) → aldehyde → least steric hindrance → most reactive

• (B) CH₃COCH₃ (acetone) → ketone with two methyl groups.More hindered than aldehyde 

• (D) Ketone with one tert-butyl group → Moderately bulky ketone → Between simple and highly bulky

• (C) Ketone with two tert-butyl groups →  Highly bulky ketone → Maximum steric hindrance → Least reactive

Increasing order of reactivity toward HCN

Most steric hindrance → least reactive:

C < D < B < A