The Tris(2-thienyl)methyl Cation Problem. A Nuclear Magnetic Resonance Spectroscopic Study

Article abstract of DOI:10.1021/jo00010a011

A series of homologues of the trityl cation obtained by total or partial substitution of the phenyl rings for 2- or 3-thienyl groups has been studied by 1H and 13C NMR.In general, the spectral parameters found follow the expected trends.However, a most unexpected effect is found in the transformation of tris(2-thienyl)carbinol (1d) into tris(2-thienyl)methyl cation (2d) , since the increase of the total chemical shift (ΔΣδ) associated with the ionization is as low as 105 ppm.To account for this observation, several hypotheses are discussed including the possibility of through-space charge delocalization by the three sulfur atoms and the interaction of the thiophene rings in an alternate conformation.