Conformational properties of trans-2-halo-acetoxycyclohexanes: 1H NMR, solvation and theoretical investigation

Conformational analyses of trans-2-halo-acetoxycyclohexanes have been performed through NMR, theoretical calculations and solvation theory. The solvent dependence of coupling constants analysed together with solvation parameters of the main calculated geometries allowed the determination of both the individual couplings and difference energies between the possible ax–ax and eq–eq conformations. For all the halo-compounds eq–eq is the most stable form in the vapour phase and in solution. The molar fractions (naa) of the ax–ax conformer are 0.28, 0.30, 0.28 and 0.22 in the vapour phase for fluoro (1), chloro (2), bromo (3) and iodo (4) derivatives, respectively, decreasing to 0.06, 0.10, 0.12 and 0.12 in DMSO, calculated through MODELS and BESTFIT, using the solvation theory. The governing factors of these conformational equilibria are the classical steric and electrostatic interactions, as well as the ‘gauche effect’, especially for the fluoro compound. The acetoxy group effect has also been compared with previous results for the hydroxy and methoxy derivatives. q 2004 Elsevier B.V. All rights reserved.