Difficult
Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions.
$(i)$ Ethanal,Propanal,Propanone,Butanone.
$(ii)$ Benzaldehyde,$p-$Tolualdehyde,$p-$Nitrobenzaldehyde,Acetophenone.
Hint: Consider steric effect and electronic effect.
$(i)$ Ethanal,Propanal,Propanone,Butanone.
$(ii)$ Benzaldehyde,$p-$Tolualdehyde,$p-$Nitrobenzaldehyde,Acetophenone.
Hint: Consider steric effect and electronic effect.
(N/A) $(i)$ The $+I$ effect of the alkyl group increases in the order: $\text{Ethanal} < \text{Propanal} < \text{Propanone} < \text{Butanone}$.
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: $\text{Butanone} < \text{Propanone} < \text{Propanal} < \text{Ethanal}$.
$(ii)$ 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 $p-$Tolualdehyde because of the presence of the electron-donating $-CH_3$ group and the lowest in $p-$Nitrobenzaldehyde because of the presence of the electron-withdrawing $-NO_2$ group. The electron-withdrawing group increases the electrophilicity of the carbonyl carbon.
Hence,the increasing order of the reactivities of the given compounds is: $\text{Acetophenone} < p-\text{Tolualdehyde} < \text{Benzaldehyde} < p-\text{Nitrobenzaldehyde}$.
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: $\text{Butanone} < \text{Propanone} < \text{Propanal} < \text{Ethanal}$.
$(ii)$ 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 $p-$Tolualdehyde because of the presence of the electron-donating $-CH_3$ group and the lowest in $p-$Nitrobenzaldehyde because of the presence of the electron-withdrawing $-NO_2$ group. The electron-withdrawing group increases the electrophilicity of the carbonyl carbon.
Hence,the increasing order of the reactivities of the given compounds is: $\text{Acetophenone} < p-\text{Tolualdehyde} < \text{Benzaldehyde} < p-\text{Nitrobenzaldehyde}$.
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