Spectroscopic studies of molecular conformations and interactions

Abstract

The first part of the thesis shows how nuclear magnetic resonance can he used to determine the energy difference between the two conformers of mono-substituted cyclohexanes or tetrahydropyrans. Proton magnetic resonance and 13Carbon magnetic resonance were used and the recently introduced Fourier transform Carbon magnetic resonance was assessed to see if it was suitable for this kind of work. It was found that the halogeno tetrahydropyran molecules studied have similar free energy differences to those of their cyclohexane analogues. Force field refinement work was carried out using biphenyl and fluorinated and deuterated derivatives including a new compound, 4-4' difluoro biphenyl d8. The restriction that all ring C-C stretch force constants should be the same was lifted and the geometry used in the calculations was improved. The dihedral angle of 4-4' difluorobiphenyl d8 in solution was estimated. Finally variable temperature studies were carried out on the infrared band shape of the YCH mode of p'difluorobenzene in cyclohexane and acetonitrile. The band was found to be broader in acetonitrile and to show a much smaller temperature dependence in the polar solvent. This is interpreted as due to vibrational relaxation governing the band width in the polar situation.