Structure and Barrier to Internal Rotation of Biphenyl Derivatives in the Gaseous State. Part 6. On the Molecular Structure and Internal Rotation of 2,2'-Bipyridine.

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Abstract
The gas-phase electron diffraction structure of 2,2''-bipyridine has been determined. Both static and dynamic models have been applied. The dynamic model is used to study the large-amplitude motion about the inter-ring C-C bond. The structure parameters (ra/.ANG. and .ltbbrac..alpha./.degree.) for the dynamic model were found to be: r(C-C)ave = 1.389(2), r(C-N)ave = 1.352(4), r (C2-C2'') = 1.496(3), r(C-H)ave = 1.108(3), and .ltbbrac.C2'' C2N1 = 116.1(5), .ltbbrac.C2N1C6 = 116.2(7), .ltbbrac.N1C6C5 = 124.6(6), .ltbbrac.C2''C2C3 = 120.9(3). The numbers in parentheses are one standard deviation as given by least-squares refinement using diagonal weight matrix. The most abundant stable conformation is the anti form. However, a less abundant conformation rotated about 120.degree. from the anti form is indicated by both the static and dynamic models. The results obtained by the electron diffraction method are in good agreement with results both from X-ray and ab initio calculations. Experimental evidence suggests that the potential energy function for internal rotation about the inter-ring bond is different in the gaseous and liquid states, with a stronger stabilization of the syn form in the liquid state.

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