Correct order of decreasing reactivity towards nucleophilic addition reaction is:
A. Acetone
B. Formaldehyde
C. Acetaldehyde
D. Acetophenone
E. Benzophenone
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B > C > A > D > E
Reactivity towards nucleophilic addition depends on how positive and how accessible the carbonyl carbon is:
Electronic effect: alkyl groups release electrons (+I) and reduce the positive charge on the C=O carbon; a phenyl group conjugated with C=O reduces it further by resonance.
Steric effect: larger groups hinder the approach of the nucleophile.
B Formaldehyde HCHO (two H) > C Acetaldehyde \( \ce{CH3CHO} \) (one \( \ce{CH3} \)) > A Acetone \( \ce{(CH3)2CO} \) (two \( \ce{CH3} \)) > D Acetophenone \( \ce{C6H5COCH3} \) (one phenyl, resonance) > E Benzophenone \( \ce{(C6H5)2CO} \) (two phenyls)
NCERT (2026-27 edition):
Reactivity – “Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. Sterically, the presence of two relatively large substituents in ketones hinders the approach of nucleophile to carbonyl carbon than in aldehydes having only one such substituent. Electronically, aldehydes are more reactive than ketones because two alkyl groups reduce the electrophilicity of the carbonyl carbon more effectively than in former.”