Read the following passage and answer the next five questions based on it.
Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. Sterically, the presence of two large groups in ketones hinders the attack of nucleophile to carbonyl carbon than in aldehydes. Electronically, aldehydes are more reactive than ketones because two alkyl groups reduce the electrophilicity of the carbonyl carbon more effectively than in the former.
A new C-C bond formation is possible in :
(A) Cannizzaro reaction
(B) Friedel-Crafts alkylation
(C) Clemmensen reduction
(D) Reimer-Tiemann reaction
Choose the correct answer from the options given below :
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B) and (D) only
A new C–C bond forms when a carbon group is attached to another carbon atom during the reaction.
(A) Cannizzaro reaction — Incorrect. One aldehyde molecule is reduced to the alcohol and another oxidised to the acid salt; only a hydride moves, no C–C bond is formed.
\( \displaystyle \ce{2HCHO + NaOH} \xrightarrow{\text{conc.}} \ce{CH3OH + HCOONa} \)
(B) Friedel-Crafts alkylation — Correct. The alkyl group is attached to a ring carbon, a new C–C bond.
\( \displaystyle \ce{C6H6 + CH3Cl} \xrightarrow{\text{anhyd. }\ce{AlCl3}} \ce{C6H5-CH3 + HCl} \)
(C) Clemmensen reduction — Incorrect. The C=O group is reduced to \( \ce{CH2} \); the carbon skeleton is unchanged.
\( \displaystyle \ce{R2C=O} \xrightarrow{\ce{Zn-Hg}/\text{conc. HCl}} \ce{R2CH2} \)
(D) Reimer-Tiemann reaction — Correct. A –CHO group is introduced at the ortho position of phenol, a new C–C bond to the ring.
\( \displaystyle \ce{C6H5OH} \xrightarrow[\text{(ii) }\ce{H+}]{\text{(i) }\ce{CHCl3}/\ce{NaOH}} \text{salicylaldehyde} \)