Nuclear magnetic resonance in some hydrocarbons at low temperatures
Abstract
The nuclear resonance absorption spectrum of several hydrocarbons has been studied at temperatures down to 20°K, using the bridge method of detection. A special cryostat was constructed for use with liquid hydrogen. In the case of cyclopentene, experimental evidence has been found in favour of a non-planar molecule, rotating about an axis perpendicular to the plane defined by four of the carbon atoms. This motion starts near 87°k, the temperature of the reported specific heat transition. At 124°k, the molecules appear to diffuse through the lattice, so that at 128°k, 10° below the melting point, the line width is less than the field inhomogeneity. Measurements of the second moments of n-pentane, n-hexane and n-octane indicate reorientation of the methyl groups about the end C-C axes, even at 20°K. an approximate value for the height of the barrier restricting the rotation in the n-octane molecule has been determined from the spin-lattice relaxation time measurements. Second moment measurements on cyclooctatetraeene have provided strong evidence in favour of a "tub" (D2a) structure of the molecule, with conjugated double and single bonds.
Type
Thesis, PhD Doctor of Philosophy
Collections
Items in the St Andrews Research Repository are protected by copyright, with all rights reserved, unless otherwise indicated.