2-Chlorocyclohexanone, conformational equilibrium

In 1953, Corey [1] studied the conformational equilibrium of a-halocyclohexanones (a-bromo- and a-chlorocyclohexanones) since the C=0 and the C-X (X = halogen) bonds are both strongly polarized, mutually repulsive, and next to each other. The conformer having the halogen atom equatorially oriented should be destabilized due to dipolar interactions between the C-X and the C=0 dipoles which are almost coplanar and equatorially oriented, whereas the conformer having the halogen atom... 

In order to compare the shifts of flie conformational equilibrium position with solvent effects it is advisable to select species exhibiting negligible cavity effects on the equilibrium position. Two firm candidates in this respect are the conformational equilibria of 1,2,2-trichloroethane and the equilibrium between the equatorial and axial forms of 2-chlorocyclohexanone both are accurately described by our scales. ... 

The preferred conformation of 2-bromo- and 2-chlorocyclohexanones depends upon the polarity of the solvent. In solvents of low dielectric constant, the halogen substituent is more stable in the axial orientation. For example, in carbon tetrachloride the Br-axial conformation of 2-bromocyclohexanone is favored by 3 1. Optical rotatory dispersion measurements on optically active tran5-2-chloro-5-methylcyclohexanone demonstrate that the preferred conformation in octane is the one in which both the chlorine and the methyl group are axial. The conformational equilibrium is reversed in the more polar solvent methanol. 

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