Geometrical distortion caused by substituents. IV. geometry and hybridization in pyridines

Departamento de Química Física, Facultad de Química, Universidad de Santiago de Compostela, 15706, Spain.

Abstract

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 also investigated. The work continues a previous study of benzene derivatives. 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 ones were also obtained by optimization, through the whole sample. These 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. Rehybridization proved to be a useful model for interpreting angle deformation. Heteroatoms exert appreciable effects, either on geometries or on 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 relatively weak interactions among the elements disturbing the ring structure.

Résumé

La géométrie des hétérocycles aromatiques avec 1 ou 2 atomes d’azote et de leurs dérivés s’écarte considérablement de l’hexagone régulier, notamment les angles internes. Nous avons calculé des angles d’hybridation, et des géométries théoriques, au moyen d’orbitales moléculaires STO-3G localisées par la méthode de Boys, pour discuter la déformation causée par des hétéroatomes et des substituants, et en chercher une interprétation.