Studies of molecular conformations by vibrational spectroscopy

Abstract

The impact of conformational analysis in chemistry was clearly demonstrated in 1969, during the tenure of this work, when the Nobel Prize for Chemistry was awarded to Professor D. H. R. Barton. The first part of this thesis deals with the vibrational analysis of biphenyl and its 4,4,-dihalogeuo derlvstlves with respect to the dihedral angle between the two rings. It is clearly demonstrated that change in conformation for biphenyl and 4,4'-difluorobinhenyl from D (solid state) to D2 symmetry (solution, molten and gaseous states) is accompanied by changes in position and spectral activity of certain normal modes. These shifts, together with supplementary data derived from some deuterated derivatives of biphenyl, give an estimate of the dihedral angle in the solution state. The structure of 4,4'-dichioro and 4,4,-dibromobiphenyl is irrespective of phase. The second part of the thesis presents the vibrational analysis of tetrahydropyran and its 4-chloro and 4-bromo derivatives. Variable temperature NMR measurements give a quantitative estimate of the con format loaal equilibrium. The final part of this work presents the liquid band shape analysis of tine 215 cm-1 band of hexsfluorobensene in mixed benzene-cyelohexane solvents. It is shown from the computed correlation functions that vibrational relaxation occurs during the split of the hexafluorobenzene-benzene complex.