Question

Which of the following is the most reactive aldehyde towards nucleophilic addition reactions?

• A. Formaldehyde
• B. Acetaldehyde
• C. Crotonaldehyde
• D. Benzaldehyde

Hint:

Less steric hindrance + stronger electrophilicity = greater reactivity in nucleophilic addition.

Answer 1

The Correct Option is A

Step 1: Reactivity principle.
Nucleophilic addition to aldehydes depends on: - Electronic effects (electron-donating/withdrawing groups).
- Steric hindrance (bulkiness near carbonyl carbon).
Step 2: Compare aldehydes.
- Formaldehyde (\(HCHO\)): No alkyl or aryl group → least steric hindrance, highly electrophilic.
- Acetaldehyde (\(CH_3CHO\)): One \(CH_3\) group → slightly less reactive.
- Crotonaldehyde (\(CH_3CH=CHCHO\)): Conjugation with double bond → less reactive.
- Benzaldehyde (\(C_6H_5CHO\)): Conjugation with aromatic ring → strongly deactivated carbonyl carbon.
Step 3: Conclusion.
Formaldehyde is the most reactive aldehyde toward nucleophilic addition.
Final Answer: \[ \boxed{\text{Formaldehyde}} \]