THE ENERGETICALLY PREFERRED ORIENTATION OF THE HYDROXYL GROUP IN CYCLOHEXANOL - AB-INITIO AND FORCE-FIELD CALCULATIONS

Quantum chemical calculations on four isomers of cyclohexanol in its c hair form were performed in order to determine the energetically prefe rred orientation of the hydroxyl group. Basis sets of different size w ere employed to study the influence of diffuse and polarization functi ons. To elucidate the role of correlation effects the calculations wer e carried out at both the Hartree-Fock (HF) and correlated (MP2, MP4) level of db initio theory, The results of all calculations agree that at a maximum value of 2 kcal mol(-1), the energy difference between al l four isomers is small. Depending on the quality of the basis set and on the inclusion of correlation energy, the most stable isomer has it s hydroxyl group either in an axial or equatorial position. Our combin ed results converge to the point that three isomers (two equatorial an d one axial) are quite similar in energy. These conformers are separat ed from the least stable species (axial) by an energy difference of 0. 9-1.6 kcal mol(-1). (C) 1997 Elsevier Science B.V.