The +I effect of the alkyl group increases in the order: Ethanal < Propanal < Propanone < Butanone The electron density at the carbonyl carbon increases with the increase in the +I effect. As a result, the chances of attack by a nucleophile decrease. Hence, the increasing order of the reactivities of the given carbonyl compounds in nucleophilic addition reactions is:
Butanone < Propanone < Propanal < Ethanal
The +I effect is more in ketone than in aldehyde. Hence, acetophenone is the least reactive in nucleophilic addition reactions. Among aldehydes, the +I effect is the highest in ptolualdehyde because of the presence of the electron-donating −CH3 group and the lowest
in p-nitrobezaldehyde because of the presence of the electron-withdrawing −NO2 group.
Hence, the increasing order of the reactivities of the given compounds is: Acetophenone < p-tolualdehyde < Benzaldehyde < p-Nitrobenzaldehyde
