A dipole moment puzzle

Abstract

The centrosymmetric compound trans-1,4-dibromo-1,4-dicyanocyclohexane is unusual in that, although it would be expected to have a zero dipole moment, and this has been verified in the crystal, it has also been observed to have a significantly nonzero dipole when in solution. In addition, using NMR, ring protons that were expected to be magnetically inequivalent were found to be equivalent. An answer to these two puzzles has been found by computationally modeling its behavior when unconstrained by crystal forces.