Question

Benzaldehyde is less reactive than propionaldehyde. Why?

Answer 1

When the benzene rings of benzaldehyde are connected with carbonyl carbon, the molecule's polarity decreases. Because benzene resonates, the positive charge spreads throughout the molecule. As a result, it is less reactive to nucleophile-based reactions.

In the case of propionaldehyde, polarity has an impact rather than any resonance effect. As a result, benzaldehyde's carbonyl carbon is less electrophilic than that of propionaldehyde. Thus, propionaldehyde is more reactive than benzaldehyde.