Molecular Structure and Crystal packing of five 4- Aminophenyl (4'-Substituted Phenyl)Sulfones. Correlations between Structural Distorsion,Spectroscopic Parameters and Electronic Substituent Effects.

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 sigma(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 pi-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-amino-phenylsulfonyl moieties forming linear chains or bidimensional networks of pi-resonant hydrogen bonds linking the molecules by means of N-H ... O=S 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.