A conformational analysis of the six isomers of bipyridinium dication

The conformational analysis of the bipyridinium dications have been investigated using ab initio STO‐3G calculations in which the inter‐ring bond length was optimized at each torsional angle. The variation of the inter‐ring separation has been rationalized using a heuristic valence bond model (which is electrostatic in nature) and which was suggested by the molecular orbital calculations. Furthermore, all six isomers show a double potential minima at the optimium torsional angles of ∼ 50° and ∼ 130° respectively. Moreover, all barrier heights are calculated to be less than 8 kJ mol−1, thereby suggesting that the barrier heights are not large enough to prevent rapid interconversion between different rotamers.