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Chapter 19: Problem 431

Suggest a reason for the observed stabilities of the two enolates of 2 -methylcyclohexanone

Short Answer

Expert verified
The observed stabilities of the two enolates of 2-methylcyclohexanone can be attributed to the differences in resonance stabilization and inductive effects. Enolate 1 has strong resonance stabilization due to the delocalization of the negative charge on the oxygen atom through the carbonyl group, and its negative charge is further stabilized by the inductive effect from the adjacent methyl group. In contrast, enolate 2 has less resonance stabilization due to steric hindrance from the C3 methyl group, making it less stable compared to enolate 1.

Step by step solution

01

Draw the Structure of 2-Methylcyclohexanone and Its Enolates

First, let's draw the structure of 2-methylcyclohexanone and convert it into its enolate forms. The structure of 2-methylcyclohexanone has a six-membered cyclic structure with a carbonyl group at C2 position and a methyl substituent at C3 position. The enolate form is formed by deprotonating the α-hydrogen of a carbonyl compound (in this case, 2-methylcyclohexanone). There are two possible enolates for 2-methylcyclohexanone - one deprotonated α-hydrogen at the C1 position, and another deprotonated at the C3 position.
02

Identify Differences in the Structures of the Two Enolates

Now that we have the structures of the two enolates, we must identify any differences in their structures that could affect the stability of the enolates. Enolate 1 (with the deprotonated α-hydrogen at the C1 position) generates a negative charge on the oxygen atom, which can be delocalized through resonance onto the carbonyl carbon (C2) and further stabilized through inductive effect from the C3 methyl group. Enolate 2 (with the deprotonated α-hydrogen at the C3 position) also generates a negative charge on the oxygen atom, but with less delocalization due to the presence of the methyl group at C3 position, causing steric hindrance.
03

Compare the Stabilities of the Two Enolates

After identifying the structural differences between the two enolates, we can now compare their stabilities. Enolate 1 has strong resonance stabilization due to the delocalization of the negative charge on the oxygen atom through the carbonyl group. Additionally, enolate 1's negative charge is further stabilized through the inductive effect from the adjacent methyl group. On the other hand, enolate 2 has less resonance stabilization due to steric hindrance from the C3 methyl group. Therefore, enolate 1 is more stable than enolate 2.
04

Suggest a Reason for the Observed Stabilities of the Two Enolates

Based on the analysis, the reason for the observed stabilities of the two enolates of 2-methylcyclohexanone can be attributed to the differences in resonance stabilization and inductive effects. Due to the presence of delocalization of the negative charge and the inductive effects from the neighboring methyl group, enolate 1 is more stable than enolate 2. In enolate 2, the steric hindrance from the adjacent methyl group reduces the resonance stabilization, making it less stable compared to enolate 1.

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