Bond angles and bond lengths in monosubstituted benzene and ethene derivatives: a comparison of computational and crystallographic results.
Bond angles and bond lengths in 29 monosubstituted benzene derivatives and in the same number of ethene derivatives were calculated at the B3LYP/6-311+G(d,p) level. Angle deformations in benzene derivatives agree reasonably with those derived statistically from the crystallographic data; in the case of small deformations, the calculated parameters are even more reliable. There is little correlation between geometry and reactivity parameters (sigma-constants) in spite of some previous claims. Nevertheless, three components of the substitution effect can be distinguished: (a) strong deformation of the adjoining angles and bonds can be ascribed to changes of hybridization; (b) a weaker effect in the meta and para positions is only partially related to resonance; (c) in the case of unsymmetrical substituents, the symmetry of the benzene ring is also broken - the angular group-induced bond alternation (AGIBA) effect. The latter effect was also confirmed by searches in the Cambridge Structural Database for alkoxy, alkylthio, acyl and azo derivatives.