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Kinetics of competitive pathways in the thermal unimolecular decomposition of hex‐1‐yne
Author(s) -
King Keith D.
Publication year - 1981
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.550130306
Subject(s) - chemistry , shock tube , propargyl , rrkm theory , thermal decomposition , decomposition , arrhenius equation , kinetics , fission , computational chemistry , reaction rate constant , activation energy , thermodynamics , organic chemistry , shock wave , catalysis , neutron , physics , quantum mechanics
The thermal unimolecular decomposition of hex‐1‐yne has been investigated over the temperature range of 903–1153 K using the technique of very low‐pressure pyrolysis (VLPP). The reaction proceeds via the competitive pathways of C 3 C 4 fission and molecular retro‐ene decomposition, with the latter being the major pathway under the experimental conditions. RRKM calculations, generalized to take into account two competing pathways, show that the experimental unimolecular rate constants are consistent with the high‐pressure Arrhenius parameters at 1100 K given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\sec ^{ - 1}) = (12.7 \pm 0.4) - (56.4 \pm 1.0)/\theta \;\;\;\hbox{for retro-ene} $$\end{document}and\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\sec ^{ - 1}) = (15.9 \pm 0.3) - (70.7 \pm 2.0)/\theta \;\;{\rm for}\;{\rm C} {-} {\rm C}\,{\rm fission} $$\end{document}where θ = 2.303 RT kcal/mol and the A factors were assigned from the results of recent shock‐tube studies of hex‐1‐yne and related alkynes. The results for CC fission are consistent with previous VLPP and shock‐tube determinations of the propargyl resonance energy, and the parameters for the molecular pathway are consistent with systematic trends for the retro–ene decomposition of unsaturated hydrocarbons.