Comparative analysis of electronic states of saturated dioxa and dithia heterocycles and their radical cations

ESR spectra of the radical cations of 1,3-dioxa- and 1,3-dithiacyclopentanes and their 2-methylated derivatives were studied both experimentally and theoretically. The orbital interaction analysis based on the localized orbital indicates that the order of the two highest occupied molecular orbitals is reversed between the dioxa and the dithia systems. It is concluded that the reversal is caused by the interaction of the orbital localized on the methylene C-H bonds of carbon atom 2 with the out-of-plane lone-pair MO composed of the lone-pair orbitals on the oxygen and the sulfur atoms. The use of the usual canonical orbital and the internally consistent SCF orbital proposed by Davidson as the base is discussed comparatively.