CONFORMATIONAL PROPERTIES OF ETHANEDIOL IN AQUEOUS-SOLUTION AS DESCRIBED BY THE CONTINUOUS MODEL OF THE SOLVENT

The description of the conformational properties of 1,2-ethanediol produced by the continuous model of the solvent at the 4-31G/SCF level is discussed. The results are compared to experimental data and to previously obtained theoretical results making use of combined Monte Carlo simulations and ab initio 6-31G* in vacuo calculations. The torsional map was determined both in vacuo and in solution. The in vacuo torsional map is generally in good agreement with the one produced by the 6-31G* basis set, which is slightly flatter. The solvation free energy, made of DELTA-G of solvation and of DELTA-E(SCF), depending on the solute conformation, is compared with the available MC results, combined with the internal energy of the solute, along the paths selected to carry out the free energy perturbation calculations (tTt --> tGg' and tGg' --> gGg'). The results of the two methods turn out to be analogous, because both favour the gauche conformers, in agreement with recent NMR data. Additional sparse ab initio calculations in solution were performed on a few selected conformations, at the 6-31G* level, in order to check the reliability of the results obtained with the 4-31G basis set. Once again, fair agreement was found among the various sets of results.