Question

The order of compounds in their reactivity towards $HCN$ is

• A. acetaldehyde < ketone < methyl fert-butyl ketone < di-tert-butyl ketone
• B. di-tert-butyl ketone < methyl tert-butyl ketone < acetone < acetaldehyde
• C. di-tert-butyl ketone < acetone < methyl tert-butyl ketone < acetaldehyde
• D. Acetone < acetaldehyde < di-tert-butyl ketone < methyl fert-butyl ketone

Answer 1

Answer: (B)

As the number/ size of alkyl group attached to the carbonyl carbon increases, their reactivity towards $HCN$ (addition-elimination reaction) decreases due to steric hindrance
Hence, the order of reactivity of different compounds towards $HCN$ is
di tert-butyl ketone < methyl tert-butyl ketone < acetone < acetaldehyde
or $[(C{H}_3{)}_{3}C{]}_{2}C=O<(C{H}_3{)}_{3}CCOC{H}_3<C{H}_{3}COC{H}_3<C{H}_{3}CHO$