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NMR Studies of the Motion of Molecules Related in Structure to Commercial Lubricants.

Luff, Stefan. (1995) NMR Studies of the Motion of Molecules Related in Structure to Commercial Lubricants. Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

A number of compounds were synthesized, including site specifically monodeuterated isotopomers, whose molecular structures parallel some of those found in commercial engineering lubricants. In the course of these syntheses, a new protocol was developed for the McMurry coupling of aliphatic ketones, involving toluene as the main reaction solvent, which gave greater economy and efficiency than those hitherto reported. Variable temperature measurements at 41.405 MHz of deuterium relaxation rates of the pure liquids of monodeuterated isotopomers 9,10-di-n-octyl-n-octadecane-9d1 9-n-octyl-n-heptadecane-9d1, and tricyclohexylmethane-d1 gave accurate values of the rotational correlation times and activation energies for isotropic overall molecular reorientation, using an analysis which assumed quadrupolar relaxation. Measurements of silicon-29 relaxation rates for tri-n-octylsilane at 53.978 MHz determined an activation energy for isotropic overall molecular reorientation, using an analysis which included both dipolar and spin-rotational relaxation. Extensive sequences of variable temperature carbon-13 NMR measurements of longitudinal relaxation rates and NOE factors were carried out at 67.83 and 100.53 MHz on the pure liquids of 9,10-di-n-octyl-n-octadecane, 9-n-octyl-n-heptadecane, tricyclohexylmethane and 1,1,2-tricyclohexylethane, and also on a sample of tri-n-octylsilane. The carbon-13 data were analyzed by assuming carbon-proton dipolar relaxation, within the theoretical picture of Lipari and Szabo, to determine correlation times, activation energies, and generalized order parameters related to their overall and internal molecular motions. The results obtained from the analyses of the deuterium relaxation measurements on 9,10-di-n-octyl-n-octadecane-9d1, 9-n-octyl-n-heptadecane-9d1, and tricyclohexylmethane-d13 were used to describe the overall molecular motion in the corresponding carbon-13 analyses. The differing examples of molecular motion enabled a careful examination of the appropriateness of the Lipari and Szabo picture in each case, and also its limitations. The relaxation data of the cyclohexyl derivatives were well described by the original Lipari and Szabo picture. A temperature dependent generalized order parameter was used to describe the relaxation data in the n-octyl compounds, and its likely significance discussed. Estimates for the quadrupolar coupling constants in 9,10-di-n-octyl-n-octadecane-9d1, 9-n-octyl-n-heptadecane-9d1, and tricyclohexylmethane-d1, emerged from a combination of the analyses of the deuterium and carbon-13 NMR data for these compounds. (continued) X-ray crystallographic structures were determined for tricyclohexylmethane and tricyclohexylmethylchloride, and the first spectroscopic and computational studies of the tricyclohexylmethyl radical were reported. Attempts were made to devise a synthetic route to tricyclohexylmethylamine, an analogue of amantadine.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Luff, Stefan.
Date : 1995
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 1995.
Depositing User : EPrints Services
Date Deposited : 06 May 2020 12:15
Last Modified : 06 May 2020 12:18
URI: http://epubs.surrey.ac.uk/id/eprint/855797

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