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.
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) Nucleophilic addition reaction: The nucleophilic addition reaction are those reaction in which a nucleophile attacks on an electron-deficient center.
The rate of nucleophilic addition reaction in carbonyl compound decrease with an increase in electron density on carbonyl carbon.
The inductive(+I) increase the electron density on the carbonyl carbon atom. The higher the length of the alkyl group attached, the greater will be the electron donation to the carbonyl carbon.
The increasing order of +I - effect on the given compound:
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
(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 methyl(−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
(i) Nucleophilic addition reaction: The nucleophilic addition reaction are those reaction in which a nucleophile attacks on an electron-deficient center.
The rate of nucleophilic addition reaction in carbonyl compound decrease with an increase in electron density on carbonyl carbon.
The inductive(+I) increase the electron density on the carbonyl carbon atom. The higher the length of the alkyl group attached, the greater will be the electron donation to the carbonyl carbon.
The increasing order of +I - effect on the given compound:
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
(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 methyl(−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
