Question

Three of the following four reactions are due to one similar feature of carbonyl compounds, while the fourth one is different. Which one is fourth?

• A. Haloform reaction
• B. Aldol condensation
• C. Knoevenagel reaction
• D. Witting reaction

Answer 1

Answer: (D)

Witting reaction

Halofrom reaction, aldol condensation, and Knoevenagel reaction involve the formation of a resonance stabilized anion, while the Witting reaction involves the addition of a nucleophile on the carbonyl carbon.

The driving force for the Witting reaction is the formation of a very strong $P-O$ bond.

Hence, the correct option is $\text{D}$