AB-INITIO STUDY OF THE STRUCTURES OF POLYTHIONYLPHOSPHAZENE MOLECULAR MIMICS WITH H, CL, AND CH3 SIDE-GROUPS - 3-21G-ASTERISK AND 6-31G-ASTERISK BASIS-SETS COMPARISON

The stable structures of substituted polythionylphosphazene single chains have been modeled with small molecular compounds consisting of one repeat unit of the polymer. The geometrical parameters of the nonplanar ''trans-cis'' conformations of these molecular models are obtained using the ab initio molecular orbital theory. The substituents studies include hydrogen and chlorine atoms and methyl groups. Two basis sets, 3-21G* and 6-31G*, were used in the computations. We have found a very good agreement between the molecular geometries obtained from the two basis sets computations for the methyl-substituted model compounds. The agreement is not as good for the hydrogenated and especially for the chlorinated model compounds. The comparison seems to indicate that the 6-31G* is an essential basis set for the chlorinated compounds. The magnitude of the total dipole moments for these compounds ranges between 3.7 and 7.9 Debye. (C) 1995 John Wiley & Sons, Inc.