Molecular structure and crystal packing of five 4-aminophenyl (4-substituted phenyl) sulfones. Correlations between structural distortions, spectroscopic parameters and electronic substituent effects

Abstract

The crystal structures of five 4-aminophenyl 4-X-phenyl sulfones (X = NO₂, CN, F, OCH₃, NH₂) are reported. The molecules present a relevant degree of charge redistribution where electronic charge transfer mainly occurs from the amino to the sulfonyl group with consequent shortening of C–N and C–S distances and increase of the quinoid character of the phenylene group. The p-aminophenylsulfonyl moiety is characterized by a substantial geometrical constancy in spite of the fact that the p-X-phenyl group is able to modulate the properties of the whole molecule as shown by the strict intercorrelation between the Hammett constant σ_p of the substituent X on one side and the proton NMR chemical shift of the p-amino group on the other side. The electronic effects of X are transmitted without increasing the quinoid character of the attached phenylene, and change only its S–C distance. This suggests an inductive charge transfer, without resonance components, from X to the SO₂ sulfur, whose partial charge can modulate the properties of the terminal aminic group through the almost constant π-delocalization of the p-aminophenylsulfonyl moiety. A detailed analysis of the hydrogen bonds present in the packing of the five crystals has been carried out. It is shown that the hydrogen bond scheme is mainly controlled by p-aminophenylsulfonyl moieties forming linear chains or bidimensional networks of π-resonant hydrogen bonds linking the molecules by means of N–H ⋯ OS interactions. The N ⋯ O distances and the IR frequencies show that these hydrogen bonds are rather weak and similar to those found in p-nitroaniline derivatives.