CONFORMERS, ENERGETICS, AND BASICITY OF 2,2'-BIPYRIDINE

摘要

The proton affinities of the cis and trans conformers of 2,2'-bipyridine have been determined at the MP2/6-31G**//HF/6-31G** level of theory. The neutral molecule and its protonated cation are both shown to possess stable cis and trans conformers: the barriers for cis/trans interconversion, and the roles that electrostatic interactions and pi-conjugation play in these barriers, are analyzed. In addition, the barriers to rotation through planar structures are reported. The structures, the effect of electron correlation on the energetics, and the ground state charge distributions are discussed (i) with respect to biphenyl and 2,2'-bipyrimidine and (ii) in the context of dinitrogen proton sponges. With regard to (i) and cis --> trans interconversion, it appears that biphenyl, 2,2'-bipyridine, and 2,2'-bipyrimidine have almost identical conformers and rotational energetics. With regard to (ii), these results indicate that SCF estimates of proton affinities and proton transfer barriers in such compounds are overestimated (by 1-2% and similar to 100%, respectively), and that barriers to rotation are underestimated by some 20-30%.