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Kinetics and Mechanisms for the Reactions of Phenyl Radical with Ketene and its Deuterated Isotopomer: An Experimental and Theoretical Study
Author(s) -
Choi Y. M.,
Lin M. C.
Publication year - 2004
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.200300919
Subject(s) - chemistry , ketene , kinetic isotope effect , reaction rate constant , arrhenius equation , transition state theory , isotopomers , thermochemistry , ab initio , hydrogen atom abstraction , deuterium , kinetics , atmospheric temperature range , chemical kinetics , reaction mechanism , benzene , activation energy , radical , computational chemistry , thermodynamics , molecule , medicinal chemistry , organic chemistry , catalysis , atomic physics , physics , quantum mechanics
Abstract Kinetics and mechanism for the reaction of phenyl radical (C 6 H 5 ) with ketene (H 2 C β C α O) were studied by the cavity ring‐down spectrometric (CRDS) technique and hybrid DFT and ab initio molecular orbital calculations. The C 6 H 5 transition at 504.8 nm was used to detect the consumption of the phenyl radical in the reaction. The absolute overall rate constants measured, including those for the reaction with CD 2 CO, can be expressed by the Arrhenius equation k =(5.9±1.8)×10 11 exp[−(1160±100)/ T ] cm 3 mol −1 s −1 over a temperature range of 301–474 K. The absence of a kinetic isotope effect suggests that direct hydrogen abstraction forming benzene and ketenyl radical is kinetically less favorable, in good agreement with the results of quantum chemical calculations at the G2MS//B3LYP6‐31G(d) level of theory for all accessible product channels, including the above abstraction and additions to the C α , C β , and O sites. For application to combustion, the rate constants were extrapolated over the temperature range of 298–2500 K under atmospheric pressure by using the predicted transition‐state parameters and the adjusted entrance reaction barriers E α = E β =1.2 kcal mol −1 ; they can be represented by the following expression in units of cm 3 mol −1 s −1 : k α =6.2×10 19 T −2.3 exp[−7590/ T ] and k β =3.2×10 4 T 2.4 exp[−246/T].