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Physicochemical Properties of Deuterated Compounds. 8 th Communication . The kinetic isotope effect for the reaction of hydrogen atoms with methylcyclohexane and perdeuteromethylcyclohexane in the gas phase
Author(s) -
Fujisaki Noboru,
Ruf Amanz,
Gäumann Tino
Publication year - 1985
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19850680512
Subject(s) - methylcyclohexane , chemistry , kinetic isotope effect , arrhenius equation , deuterium , kinetic energy , hydrogen , hydrogen atom abstraction , thermodynamics , activation energy , computational chemistry , atomic physics , organic chemistry , catalysis , physics , quantum mechanics
Using H‐atoms produced in the radiolysis of water vapour, we determined the kinetic isotope effect for the reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm H}^{\rm .} + {\rm RH (R'D)}{\rm H}_{\rm 2} {\rm (HD) + R}^{\rm .} {\rm (R'}^{\rm .}) $$\end{document} where RH and R′D are methylcyclohexane and perdeuterated methylcyclohexane, respectively. The result obtained from the isotope competitive method can be expressed with the Arrhenius ‐type equation k H / k D = (0.51 ± 0.04) exp[(8.58 ± 0.25) kJ mol −1 / RT ] over the temperature range from 363 to 483 K. The occurrence of H abstraction from primary, secondary, and tertiary CH bonds in methylcyclohexane is taken into consideration in the interpretation of the Arrhenius ‐type expression obtained. Theoretical interpretation of the kinetic isotope effect has been achieved on the basis of the transition‐state theory and a semiempirical London ‐ Eyring ‐ Polanyi ‐ Sato potential‐energy surface. The tunnel effect is found to play a role in the H‐abstraction. Several methods for estimating the tunnel correction factors have been discussed.