Chapter 4, Problem 4.72P

Interpretation Introduction

Interpretation:

The reason for existence of both $\text{bromocyclohexane}$ and $\text{iodocyclohexane}$ with $\text{31\%}$ of molecules having halogen atom in the axial position even though an iodine atom is larger in size than a bromine atom is to be explained.

Concept introduction:

A monosubstituted cyclohexane is more stable when the bulkier substituent occupies an equatorial position. The equatorial conformer is more stable than the axial conformer because there is more room for the substituent in the equatorial position. In the axial position, the substituent gets significant steric strain due to repulsion between the electrons on the axial substituents and those on the axial H atoms two positions away on the ring. This is called $\text{1, 3}$ diaxial interactions. Due to $\text{1, 3}$ diaxial interactions, the substituent prefers to occupy equatorial position to be the more stable conformation. The stability of conformer also depends on the size of the substituent and bond length between carbon and the substituent.