The crystal and molecular structure of 1,2,3,5-tetramethylbenzo[b]thiophenium tetrafluoroborate and some theoretical calculations on the hypothetical 1H-thiophenium cation

Abstract

The X-ray crystal structure of 1,2,3,5-tetramethylbenzo[b]thiophenium tetrafluoroborate, refined to R 0.043, shows the bonding about sulphur to be pyramidal and not planar. This structure and the ¹³C n.m.r. spectral data suggest that benzo[b]thiophenium salts should be considered as cyclic styrene derivatives. Theoretical calculations also showed an energy maxium for the planar configuration of the 1H-thiophenium cation.