Torsional barriers in biphenyl, 2,2 '-bipyridine and 2-phenylpyridine

The rotational barriers for biphenyl, 2,2'-bipyridine and 2-phenylpyridine were calculated with HF, B3LYP, BPW91, and MP2 and double-zeta polarized ba sis sets. The methods differ significantly in the near-planar region, and a re in close agreement otherwise, with DFT results similar to experiment ove r the whole range (for biphenyl). Steric repulsions, stabilizing C-H-N' int eractions, pi-conjugation and electron correlation give rise to DFT-calcula ted dihedrals for biphenyl of about 40 degrees and similar 0 degrees and 90 degrees barriers, dihedrals of 23 degrees and an almost non-existent 0 deg rees barrier for 2-phenylpyridine and two minima for 2,2'-bipyridine, which is strongly stabilized by two C-H-N' interactions in the coplanar conforma tion with anti-standing nitrogens. (C) 2000 Elsevier Science B.V. All right s reserved.