Q44. Which of the following is most reactive towards nucleophilic addition reaction?
(a) Butanone
(b) Propanone
(c) Ethanal
(d) Propanal

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FirstInTest · Accepted Answer

Correct answer: C. The reactivity of carbonyl compounds towards nucleophilic addition reactions is determined by two main factors: steric hindrance and electronic effects.1. Steric hindrance: Less bulky groups around the carbonyl carbon lead to higher reactivity.2. Electronic effects: Electron-donating alkyl groups (+I effect) decrease the electrophilicity of the carbonyl carbon, thus decreasing reactivity. Electron-withdrawing groups increase reactivity.Comparing the given compounds:(a) Butanone (CH3CH2COCH3): A ketone with two alkyl groups (one ethyl, one methyl), creating significant steric hindrance and electron donation.(b) Propanone (CH3COCH3): A ketone with two methyl groups, more steric hindrance and electron donation than aldehydes.(c) Ethanal (CH3CHO): An aldehyde with one methyl group and one hydrogen. Less steric hindrance and less electron donation than ketones or larger aldehydes.(d) Propanal (CH3CH2CHO): An aldehyde with one ethyl group and one hydrogen. More steric hindrance and electron donation than ethanal, but less than ketones.Aldehydes are generally more reactive than ketones due to less steric hindrance and weaker +I effects. Among aldehydes, ethanal is the least hindered and has the weakest +I effect from the methyl group compared to the ethyl group in propanal.Therefore, Ethanal is the most reactive towards nucleophilic addition reactions.

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