Molecular geometry of substituted benzene derivatives. IV. Analysis of variance in monosubstituted benzene rings

Abstract

The variance of the geometry of monosubstituted benzene rings has been analysed systematically from a sample of 199 rings, representing a wide spectrum of substituents. The sample is composed of structures determined accurately by X-ray crystallography, neutron crystallography and microwave spectroscopy. Part of the analysis has been carried out using symmetry coordinates based on the irreducible representations of the D6h point group. The application of bivariate analysis to these coordinates shows that the angular variance of monosubstituted benzene rings is fully described by two orthogonal components of distortion, involving angular changes in different ratios. The distortion that accounts for most of the variance is a simultaneous change of the internal angles at the ipso, ortho and (to a minor extent)para positions of the ring, and is definitely related to the tr electronegativity of the substituent. The second distortion involves mainly the internal angles at the meta and para positions and is controlled to a large extent by the n-donor/acceptor power of the substituent. The separation of the two distortions is not based on chemical assumptions, but stems directly from the statistical analysis of the data. When bond-length variation is included in the model, factor analysis reveals the existence of three orthogonal components of distortion. These account for ca 90% of the variance, the remaining 10% being essentially due to random experimental error. The first distortion, accounting for ca 40% of the variance, now also involves a change of the Ctpso-Corth o bond length. The second distortion accounts for ca 20% of the variance

Crystal chemistry of tetraradial species. Part 7. Lithium tetrakis(1-imidazolyl)-borate solvate, Liiv[Liiv(H2O)(MeOH)]-[B(C3H3N2)4]2•MeOH, a 3-dimensional polymer; with observations on the geometry of imidazole rings

“…Among the substituents represented in the sample the NO, group is the most powerful expander and the anionic B atom the most powerful contractor of the ipso angle in the ring. The general conclusions parallel those formulated for substitutions in benzene by Domenicano et al (22)(23)(24)(25), but important differences arise from the heterocyclic and oddmember character of the imidazole ring.…”

“…This is due to the impossibility of satisfying cyclic sign alternation of A+i in an odd-membered planar ring. In this respect the effects of substitution on the +i in Im differ from those in benzene, investigated by Domenicano et al (22)(23)(24)(25).…”

“…It does not include structures in which Im is a ligand to a (heavy) metal atom in a discrete coordination complex or in which the Im ring is part of a larger fused ring system. (24) 10973 (4) 6366 (3) 9453 (4) N (73) 1098 (3) 3852 (2) 8058(3) C (25) 10806 (4) 680 (3) 7982 (3) 4653 (4) N (83) 1573 (3) 5458 (2) 3349(3) C (35) 11677 (3) 8429 (3) 5838 (4) C (84) 1807 (3) 4572 (3) 2989(4) N (41) 10594 (2) 9398 (2) 7863 (3) (43) 11832 (3) 10470 (2) 9033 (4) Li (2) 5637 (5) 8293 (4) 7533 (7) C (44) 10942 (4) 5 1) 3936 (2) 5680 (2) 7393 (3) O(m2) 5879 (2) 10938 (2) 6573(3) C (52) 4533 (3) 6313 (3) 6854 (4) C(m2) 6855 (4) Table C. the lines of the classical investigations of Domenicano et al (22)(23)(24)(25) into the geometrical effects of substitution in benzene is precluded here part...…”

Structural studies of organoboron compounds. XXVI. 8-Methyl-6,6-diphenyl-5,7-dioxa-8-azonia-6-borata-6,7-dihydro-5H-benzocycloheptene

“…This distance, which corresponds to a van der Waals contact, is probably sufficiently short to facilitate the 1,4-migration of the phenyl group via a transition state 2. The aromatic rings in 1 are all planar to within experimental error, their geometry being consistent with normal substituent effects (16).…”

Structure of 4-[(2-benzoyl-1-methyl)vinyleneimino]butyric acid

“…The phenyl group presents normal values for bond lengths and angles, corresponding to the substitution pattern (Domenicano, Murray-Rust & Vaciago, 1983).…”