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The addition of methyl radicals to hexafluoroacetone
Author(s) -
Batt L.,
Mowat S. I.
Publication year - 1984
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.550160509
Subject(s) - hexafluoroacetone , chemistry , radical , trifluoromethyl , torr , peroxide , hydrogen atom , hydrogen peroxide , reaction rate constant , photochemistry , medicinal chemistry , organic chemistry , kinetics , thermodynamics , group (periodic table) , alkyl , physics , quantum mechanics
The reaction of methyl radicals (Me) with hexafluoroacetone (HFA), generated from ditertiary butyl peroxide (dtBP), was studied over the temperature range of 402–433 K and the pressure range of 38–111 torr. The reaction resulted in the following displacement process taking place:where TFA refers to trifluoroacetone. The trifluoromethyl radicals that were generated abstract a hydrogen atom from the peroxide:such that k 6a is given by:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm log}\,\,k_{6{\rm a}} \left( {M^{ - 1} \cdot {\rm s}^{ - 1} } \right)\,\, = \,\,8.2\, \pm \,0.7\, - \,8.9\, \pm \,{{1.3} \mathord{\left/ {\vphantom {{1.3} \theta }} \right. \kern-\nulldelimiterspace} \theta } $$\end{document}where θ = 2.303 RT kcal/mol. The interaction of methyl and trifluoromethyl radicals results in the following steps:Product analysis shows that k 17 / k 15 1/2k 16 1/2= 2.0 ± 0.2 such that k 17 = 10 10.4±0.5 M −1 · s −1 . The rate constant k 5 is given by:\documentclass{article}\pagestyle{empty}\begin{document}$$ {{{\rm log}\,\,k_5 } \mathord{\left/ {\vphantom {{{\rm log}\,\,k_5 } {\left( {M^{ - 1} \cdot {\rm s}^{ - 1} } \right)}}} \right. \kern-\nulldelimiterspace} {\left( {M^{ - 1} \cdot {\rm s}^{ - 1} } \right)}}\,\, = \,\,8.0\, \pm \,1.3\, - \,5.1\, \pm \,{{0.7} \mathord{\left/ {\vphantom {{0.7} \theta }} \right. \kern-\nulldelimiterspace} \theta } $$\end{document}It is concluded that the preexponential factor for the addition of methyl radicals to ketones is lower than that for the addition of methyl radicals to olefins.