Semi-empirical calculations on bis-halomethyl sulfides. A comparison of the structures and other parameters by MNDO, AM1 and PM3 methods

Abstract

Semi-empirical (MNDO, AM1 and PM3) calculations of geometry, heats of formation, ionization potential and dipole moments have been made of bis-halomethyl sulfides of the type R 1SR 3 (where R 1 = CH 3 or CF 3 and R 3 = CH 3, CH 2Cl, CHCl 2, CCl 3, CFCl 2, CF 2Cl and CF 3). Because of the lack of experimental data for some molecules, no detailed comparisons have been made between experimental and calculated data. The geometric parameters have been cross-checked with available experimental values and variations along the series. They have also been compared with molecules having similar structures such as ethers and propanes. The conformations are not well reproduced by any of the three methods in which the geometries are calculated for all the molecules on the basis of an eclipsed conformation and without later restrictions in the optimization calculation. The heats of formation are best reproduced by the AM1 method and ionization potentials, in contrast, by the PM3 method.