Question

Aromatic aldehydes are less reactive than the aliphatic aldehydes in nucleophilic addition reaction this is due to

• A. electron donating resonance effect of aromatic ring
• B. electron withdrawing resonance effect of aromatic ring
• C. carbonyl carbon is less nucleophilic
• D. Presence of two alkyl group.

Hint:

The ring donates electron density to the carbonyl carbon by resonance.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
Nucleophilic addition depends on how positive (electrophilic) the carbonyl carbon is.
The more electron-deficient it is, the faster the nucleophile attacks.

Step 2: Effect of the ring
In benzaldehyde the C=O group is conjugated with the benzene ring.
The ring pushes \(\pi\) electron density towards the carbonyl group by the +R (electron donating resonance) effect.

Step 3: Result
The partial positive charge on carbon decreases, so nucleophiles attack less readily than in aliphatic aldehydes.

Step 4: Compare the options
Option (B) is the opposite effect.
The carbonyl carbon is electrophilic, not nucleophilic, so (C) is wrong.
Aldehydes do not have two alkyl groups, so (D) is wrong.

Final Answer:
The lower reactivity is due to the electron donating resonance effect of the aromatic ring, option (A). \[ \boxed{\text{(A) }\text{electron donating resonance effect of aromatic ring}} \]