Aldehydes And Ketones

- Aqueous KOH favors nucleophilic substitution (SN1/SN2) reactions, where OH− acts as a nucleophile, forming alcohols.
- Alcoholic KOH, due to the presence of alkoxide ions (RO−), is a stronger base and favors the elimination (E2) reaction, leading to alkene formation.

Grignard reagents (RMgX) are highly reactive towards moisture. If water is present, it reacts with the Grignard reagent, forming an alkane instead of undergoing the desired reaction. This is why anhydrous conditions are necessary during preparation and storage.

Why Benzaldehyde is Less Reactive than Propanal in Nucleophilic Addition Reactions

Benzaldehyde is less reactive in nucleophilic addition reactions than propanal due to the presence of a resonance-stabilized benzene ring attached to its carbonyl group.

In benzaldehyde, the carbonyl carbon is less electrophilic because of resonance interaction between the carbonyl group and the aromatic ring:

This delocalization reduces the partial positive charge on the carbonyl carbon, making it less susceptible to nucleophilic attack.

In contrast, propanal ( ) has no such resonance stabilization. The electron-withdrawing nature of the carbonyl group is unopposed, so the carbonyl carbon remains strongly electrophilic and readily undergoes nucleophilic addition.

Conclusion:

Benzaldehyde: Reactivity reduced due to resonance with benzene ring.
Propanal: More reactive as no resonance stabilization exists.