Read the Passage carefully and answer the questions.
The carbonyl group of aldehydes and ketones is highly polar. The positively charged carbon is readily attacked by electron-rich nucleophile and the negatively charged oxygen atom is attacked by an electro-deficient electrophile. Aldehydes and ketones undergo nucleophilic addition reactions in the presence of acid or a base. The mechanism involves attack of a nucleophile on the electron deficient carbonyl carbon to form a tetrahedral intermediate. A new bond is formed between the carbon and oxygen. Protonation of the anion furnished by the reaction medium yields a neutral addition product. The addition product is same whether the reaction is catalyzed by acid or a base. For example in the presence of base aldehydes and ketones react with hydrogen cyanide to form cyanohydrin.
Which of the following compounds will undergo nucleophilic addition readily?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → Formaldehyde **
Nucleophilic addition to a carbonyl compound is favored when:
- Steric hindrance is minimum
- +I / electron-donating effects are minimum
- Carbonyl carbon is most electrophilic
Comparison of options:
- Formaldehyde (HCHO) → no alkyl groups, least steric hindrance, highest electrophilicity
- Acetaldehyde (CH₃CHO) → one alkyl group
- Benzaldehyde (C₆H₅CHO) → resonance donation from phenyl ring reduces electrophilicity
- Butanone (CH₃COC₂H₅) → ketone + steric hindrance
Hence Formaldehyde is the correct answer