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Intramolecular isotopic effect in the pyrolysis of ethyl‐2 d 1 chloride
Author(s) -
Papagiannakopoulos P. J.,
Benson S. W.
Publication year - 1982
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550140108
Subject(s) - chemistry , intramolecular force , arrhenius equation , kinetic isotope effect , branching (polymer chemistry) , thermal decomposition , branching fraction , atmospheric temperature range , deuterium , decomposition , reaction rate constant , rrkm theory , analytical chemistry (journal) , thermodynamics , kinetics , stereochemistry , atomic physics , organic chemistry , activation energy , physics , quantum mechanics
The thermal decomposition of deuterated ethyl chloride CH 2 DCH 2 Cl was studied in a static system in the pressure range of 0.1–26 torr, and the Arrhenius expression for the overall decomposition at the high‐pressure limit and in the temperature range of 670–1100 K was found to be\documentclass{article}\pagestyle{empty}\begin{document}$$ k_\infty = 10^{13.33 \pm 0.10} \exp [(- 57,200 \pm 500){\rm cal/mol/}RT]{\rm}s^{- 1} $$\end{document}The intramolecular isotopic effects were first examined in the pressure range of 0.1–26 torr at 837 K, and the branching ratio k H / k D was found to decrease with increasing pressure. The RRKM‐theory calculations describe the experimental data well. The intramolecular isotopic effect was also examined in the temperature range of 728–926 K, and the branching ratio at the high pressure limit was given by the expression\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm H} /k_{\rm D} = (1.44 \pm 0.05)\exp [(1500 \pm 50){\rm cal/mol/}RT] $$\end{document} when k H and k D are the rate constants for the HCl and DCl channels of elimination. The Arrhenius A factors obtained at the high‐pressure limit together with the temperature‐dependent expression of the branching ratio provided additional experimental data for an assignment (fine‐tuned) of the vibrational frequencies of both activated complexes involved in the thermal decomposition of CH 2 DCH 2 Cl. The evaluated vibrational frequencies were then used in the RRKM calculations describing the pressure dependence of the intramolecular isotopic effect. The RRKM calculations and the experimental data were in good agreement, supporting the choice of vibrational frequencies for both the activated complexes as well as the transition‐state model.