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https://hdl.handle.net/2142/70383
Description
Title
Applications of High Pressure Dynamic NMR
Author(s)
Ashcroft, Joseph Samuel
Issue Date
1987
Doctoral Committee Chair(s)
Jonas, Jiri
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Abstract
The effects of temperature and pressure on the conformational isomerization of 1,1-difluorocyclohexane in solution have been studied using $\sp $F FT-NMR spectroscopy. The pressure dependence of the isomerization of 1,1-difluorcyclohexane in acetone-d$\sb6$, n-pentane and methylcyclohexane compared to the pressure dependence of the isomerization of cyclohexane in the same solvents indicates that intramolecular effects cause 1,1-difluorocyclohexane to isomerize as if it is in the diffusive limit region. This diffusive limit behavior is observed in all three solvents. Dielectric friction if present is not as important of an energy transfer mechanism as collisions for the 1,1-difluorocyclohexane reaction system.
The pressure dependence of the rate of isomerization of cyclohexane in pentane-d$\sb $ has been observed. The pressure dependence of the extracted k, ln k, and the volumes of activation and transmission coefficients derived from the rate constant data all qualitatively agree with previous data obtained from the cyclohexane/acetone-d$\sb6$ obtained in a previous variable pressure NMR experiment carried out in 1981. Chemical shifts in absence of exchange were extracted from the spectra along with the rate constant. No pressure dependence of the chemical shift in absence of exchange was observed. Changes in line width as a function of pressure and shimming were taken into account by observing the change in line width of the residual proton signal from undeuterated n-pentane solvent. From this it is possible to conclude that the cyclohexane/pentane-d$\sb $ system is undergoing reactions in the inertial region.
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