Question

The reactivity of the enol derivatives

towards benzaldehyde follows the order

• A. I > II > III
• B. III > II > I
• C. II > I > III
• D. I> III > II

Answer 1

The Correct Option is D

The reactivity of enol derivatives towards benzaldehyde can be understood by analyzing the nature and strength of the leaving groups in each compound. In organic chemistry, reactivity often depends on the stability of the transition state and the nature of the substituents.

1. The structures given are enolates with different substituents:
   • I: OLi (Lithium enolate)
   • II: OSiMe₃ (Silyl enolate)
   • III: OZnBr (Zinc enolate)
2. The order of reactivity towards benzaldehyde is often influenced by the strength of the metal-carbon bond. Less electronegative cations, which form more ionic bonds, tend to make the enolate stronger nucleophiles.
3. Lithium enolates (I) are the most reactive because the lithium-oxygen bond is highly ionic, leading to greater nucleophilicity compared to other enolates.
4. Zinc enolates (III) are more reactive than silyl enolates because zinc-oxygen bonds are less covalent than silicon-oxygen bonds, making them better nucleophiles than silyl enolates, which are more stable and less reactive.
5. Silyl enolates (II) are the least reactive amongst the three due to the strong covalent character of the silicon-oxygen bond, making nucleophilic attack less favorable.

Therefore, the correct order of reactivity towards benzaldehyde is: I > III > II.