Comparison of X-ray and ab initio deformation densities in dimethyl-γ-pyrone and triazine trichloride

Abstract

Deformation density contour maps for dimethyl-γ-pyrone and for triazine trichloride derived both from X-ray diffraction intensity measurements and from ab initio electronic structure calculations are reported and a detailed comparison discussed. There is generally good agreement between the X-ray and ab initio maps when the electronic structure calculation employs a polarization basis set. Only very gross features of agreement are seen between the maps when split valence basis sets are used. Different regions of the molecule fare differently, but reasonably secure uniform agreement over the majority of the molecular density is obtained with the polarization basis set. The hierarchy of basis sets examined range over STO-3G, 3-21G, 4-31G, 6-31G and 6-31G ∗. Both approaches show extensive delocalization of the π electron system of these molecules.