Question

Arrange the following compounds in increasing order of their reactivity in nucleophilic addition reactions.

$A$: Ethanal, Propanal, Propanone, Butanone.


$B$: Benzaldehyde, p-Tolualdehyde, p-Nitrobenzaldehyde, Acetophenone.

Answer 1

$A$:
The given compounds are represented as -


From the above structures, we can see that, due to $+I$ effect of alkyl group the electron density at carbonyl carbon increases from ethanal to butanone.
The steric crowding also increases in this order.
Lesser electron density and lesser steric crowding favours reactivity towards a nucleophile.
Thus, the increasing order of reactivity towards nucleophile is given below-
$\text{Butanone}<\text{propanone}<\text{propanal}<\text{ethanal}$

$B$:

Presence of electron withdrawing group deceases electron density at carbonyl carbon and make carbonyl more reactive towards nucleophilic addition reactions.
So, $-I$ effect favours but $+I$ effect disfavours this reaction.
Increasing order of reactivity of these compounds given below as per above conditions-
$\text{Acetophenone}<\text{p-tolualdehyde}<\text{benzaldehyde}<\text{p-nitrobenzaldehyde}$