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Author Hasha, D. L. ♦ Eguchi, T. ♦ Jonas, J.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY ♦ CYCLOHEXANE ♦ ISOMERIZATION ♦ ACETONE ♦ ACTIVATION ENERGY ♦ CARBON SULFIDES ♦ CHEMICAL REACTION KINETICS ♦ CYCLOALKANES ♦ EXPERIMENTAL DATA ♦ HIGH PRESSURE ♦ LOW TEMPERATURE ♦ NMR SPECTRA ♦ NUCLEAR MAGNETIC RESONANCE ♦ ORGANIC SOLVENTS ♦ PRESSURE DEPENDENCE ♦ TEMPERATURE DEPENDENCE ♦ VERY HIGH PRESSURE ♦ ALKANES ♦ CARBON COMPOUNDS ♦ CHALCOGENIDES ♦ CHEMICAL REACTIONS ♦ DATA ♦ ENERGY ♦ HYDROCARBONS ♦ INFORMATION ♦ KETONES ♦ KINETICS ♦ MAGNETIC RESONANCE ♦ NUMERICAL DATA ♦ ORGANIC COMPOUNDS ♦ REACTION KINETICS ♦ RESONANCE ♦ SOLVENTS ♦ SPECTRA ♦ SULFIDES ♦ SULFUR COMPOUNDS ♦ Organic Chemistry- Chemical & Physicochemical Properties- (-1987) ♦ Spectral Procedures- (-1987)
Abstract The effect of temperature and pressure on the conformational inversion of cyclohexane in solution has been investigated with use of /sup 1/H FT NMR spectroscopy. The solvents used in this study are methylcyclohexane-d/sub 14/, carbon disulfide, and acetone-d/sub 6/. The activation parameters as obtained from the temperature dependence of the rate constant are independent of solvent. However, the coalescence temperature in the methylcyclohexane-d/sub 14/ solvent is 1.5/sup 0/C higher than in the other two solvents. It is observed that the ring inversion in cyclohexane is accelerated when pressure is increased, and this pressure dependence of the rate constant is nonlinear. In the lower viscosity solvents, acetone-d/sub 6/ and carbon disulfide, the rate constant shows a larger pressure dependence than in the more viscous methylcyclohexane-d/sub 14/ solvent. The experimental data are interpreted with use of results of the stochastic models for isomerization reactions. In these models it is proposed that there are dynamical effects on isomerization because the reaction coordinate is coupled to the surrounding medium. We find that the observed activation volume is strongly pressure and solvent dependent as is the collisional contribution to the activation volume. Since the collision frequency reflecting the coupling of the reaction coordinate to the solvent mediums is proportional to solvent viscosity, the observed activation volume and the transmission coefficient kappa correlate well with the solvent viscosity. In addition, the experimental data indicate a non-monotonic transition between the inertial (weak coupling) and diffusive (strong coupling) regimes of isomerization reactions. Our results represent the first experimental proof of the predictions of stochastic models for isomerization reactions in condensed phases. 9 figures, 1 table.
Educational Use Research
Learning Resource Type Article
Publisher Date 1982-04-21
Publisher Place United States
Journal J. Am. Chem. Soc.
Volume Number 104
Issue Number 8


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