The structure of 2,2′-difluorobiphenyl in solid crystalline and liquid crystalline phases

The structure of 2,2'-difluorobiphenyl in the solid, crystalline phase has been determined by X-ray diffraction. In this phase the molecules are all in a single conformation having the two fluorine nuclei in a syn-arrangment, with the two ring normals at 58 degrees to one another. The structure of the same molecule, but dissolved in a liquid crystalline solvent has been investigated by NMR spectroscopy. In the liquid crystalline phase there is rotation about the inter-ring bond through an angle phi, with a probability distribution P(phi) which has an absolute maximum at the syn-form with phi about 51 degrees. There is also a second maximum in P(phi) at about 130 degrees, corresponding to the anti-form. The syn- and anti-forms are present in the approximate ratio 0.58:0.42.