Conformational analysis of bithienyl derivatives: a liquid crystal nuclear magnetic resonance approach

The conformational analysis of three substituted 2,2′-bithienyl derivatives has been accomplished by means of the liquid crystal n.m.r. spectroscopy. The interpretation of the spectral data allows the possibility of free rotation as well as the existence of a single planar or twisted conformation to be ruled out. Models of an equilibrium between the S-trans(= 78%) and S-cis(= 22%) rotamers were in agreement with the experimental data. The results also agree with previous e.s.r. experiments and with the predictions of theoretical calculations.