Theoretical conformational analysis of p-, m-, and o-terphenyl

A ground state conformational analysis has been carried out on p-, m-, and o-terphenyl using a recently developed semiempirical calculation method (CS-INDO). The potential energy surface has been calculated as a function of the torsion angles of the two terminal phenyls relative to the central one. Two nearly isoenergetic rotamers are found to exist for both p- and m-terphenyl, at geometries corresponding to D2, and C2h symmetries for p-terphenyl, C2, and Cs symmetries for m-terphenyl. The torsion angles are ca. 35° in all cases. The barriers separating the two minima of each potential surface are low enough to allow a rapid interconversion of the rotamers at room temperature in the gas phase (they are in “dynamic” equilibrium). o-Terphenyl presents only one equilibrium geometry. These findings are compared with the results of previous experimental and theoretical studies, which are extensively reviewed.