Conformational Analysis of Cyclohexandiols and Related Compounds
The conformational equilibria in disubstituted cyclohexanes containing polar groups lead to a diversity of conformational forms. In solution, the conformational preference is shown to be highly dependent upon the nature of the solvent. In the cyclohexandiol series, the formation of intramolecular and intermolecular hydrogen bonds determines the conformational preference with regard to the molecule as a whole and with respect to the rotamer conformation of the hydroxyl groups. Polar solvents capable of hydrogen bonding to the hydroxyl group have been shown to influence the position of equilibrium between the alternative chair conformations. In cyclohexanol, the equilibrium is always shifted towards the equatorial conformation. 13C nmr, 1H nmr, solution i.r. and matrix isolation i.r. techniques have been used to determine the conformational structures in the cyclohexandiol series and the nature of the solvent interactions. Two types of solvent interaction have been identified, a hydrogen bonded interaction and a non-bonded dipole interaction. A Computer Graphic Simulation has been used to' quantify the conformational energy differences and to rationalize the experimental results in terms of the Van der Waals repulsion energy. The experimental results give strong evidence that in cis cyclohexan-1,3-diol, two types of internal hydrogen bond exist in the diaxial conformation. The Computer Graphic simulation supports this reasoning on thermodynamic grounds.
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