19P - Organic Chemistry (Mcmurry)

Question

For a given hydrogen atom to be acidic, the C-H bond must be parallel to the p orbitals of the CO double bond (that is, perpendicular to the plane of the adjacent carbonyl group). Identify the most acidic hydrogen atom in the conformation shown for the following structure. Is it axial or equatorial?

Step-by-Step Solution

Answer

Step 1: Introduction

The molecule shown in the model is 2,2-dimethylcyclohexanone.

 

The most acidic hydrogen of the given molecule is

 

The acidic hydrogen is axial.

 

Step 2: Explanation of the solution

The given molecule has two α-carbons. One α-carbon has two methyl groups, and the other α-carbon has two hydrogen atoms (axial and equatorial). The axial hydrogen atom is more acidic because its p-orbital after removal remains aligned. This will helps the optimum overlap with the π electrons of the carbonyl oxygen. 

 

 

Step 3: Conclusion

Hence, the most acidic hydrogen in the given structure is the axial hydrogen.