Question

Would you expect benzaldehyde to be more reactive or less reactive in nucleophilic addition reactions than propanal? Explain your answer.

Answer 1

Reactivity of benzaldehyde and propanal towards nucleophilic addition reaction:

Propanal is an aliphatic aldehyde and benzaldehyde is an aromatic aldehyde.
In benzaldehyde, the polarity of carbonyl group decreases due to resonance as shown below.


So, in benzaldehyde, carbon atom of the carbonyl group is less electrophilic as compared with propanal as there is no resonance in propanal. So propanal is more reactive towards nucleophilic addition reactions.