GEOMETRICAL DISTORTION CAUSED BY SUBSTITUENTS .4. GEOMETRY AND HYBRIDIZATION IN PYRIDINES

A survey on in-plane distortions involving aromatic heterocycles of 6 atoms with 1 or 2 N's with respect to benzene geometry was undertaken. Distortions of some of their derivatives with respect to these were a lso investigated. The work continues a previous study of benzene deriv atives. Hybridization angles were calculated by localized MO's, using Boys' criterion, and their relation to geometrical angles was analysed . Since detailed experimental geometries are scarce, the theoretical o nes were also obtained by optimization, through the whole sample. Thes e are in good agreement with the existent experimental determinations, what allows patterns of deformation to be examined. STO-3G basis was used, as this is convenient under the conditions of our research. Rehy bridization proved to be a useful model for interpreting angle deforma tion. Heteroatoms exert appreciable effects, either on geometries or o n hybridization angles. Substituent effects are very similar to those found in benzene, and less important than heteroatom ones. Approximate additivity was found for the different effects examined, suggesting r elatively weak interactions among the elements disturbing the ring str ucture.