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.

Explanation

(i) Reactivity of carbonyl compound `prop ` (+)ve charge on `sp^(2) C`

The +I effect of the alkyl group increases in the order :
Ethanal `lt` Propanal `lt` Propanone `lt` Butanone
If +I effect increases then (+)ve charge on `sp^(2) C ` decreases.
So reactivity order is :
Butanone `lt` Propanone `lt` Propanal `lt` Ethanal

(ii) –I group on gtC = O increases (+)ve charge so reactivity order is
Acetophenone `lt` p-tolualdehyde`lt` Benzaldehyde `lt` p -Nitrobenzaldehyde