Direct observation of the gas phase reaction of the cyclohexyl radical with dioxygen using a distonic radical ion approach

Kirk, B. B., Harman, D. G., & Blanksby, Stephen J. (2009) Direct observation of the gas phase reaction of the cyclohexyl radical with dioxygen using a distonic radical ion approach. Journal of Physical Chemistry A, 114(3), pp. 1446-1456.

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Alkylperoxyl radicals are intermediates in the oxidation Of hydrocarbons. The reactive nature of these intermediates, however, has made therin elusive to direct observation and isolation. We have employed ion trap mass spectrometry to synthesize and characterize 4-carboxylatocyclohexyl radical anions ((center dot)C(6)H(10)-CO(2)(-)) and observe their reactivity in the presence of dioxygen. The resulting reaction is facile (k = 1.8 x 10(-10) cm(3) molecule(-1) s(-1) or 30% of calculated collision rate) and results in (i) the addition Of O(2) to form stabilized 4-carboxylatocyclohexylperoxyl radical anions ((center dot)OO-C(6)H(10)-CO(2)(-)), providing the first direct observation of a cyclohexylperoxyl radical, and (ii) elimination of HO(2)(center dot) and HO(center dot) radicals consistent with recent laser-induced fluorescence studies of the reaction of neutral cyclohexyl radicals with O(2). Electronic structure calculations at the B3LYP/6-31+G(d) level of theory reveal viable pathways for the observed reactions showing that formation of the peroxyl radical is exothermic by 37 kcal mol(-1) with subsequent transition states its low as -6.6 kcal mol(-1) (formation of HO(2)(center dot)) and -9.1 kcal mol(-1) (formation of HO(center dot)) with respect to the entrance channel. The combined computational and experimental data Suggest that the structures of the reaction products correspond to cyclohexenes and epoxides from HO(2)(center dot) and HO(center dot) loss, respectively, while alternative pathways leading to cyclohexanone or ring-opened isomers ate not observed, Activation of the charged peroxyl radical (center dot)OO-C(6)H(10)-CO(2)(-) by collision induced disassociation also results in the loss Of HO(2)(center dot) and HO(center dot) radicals confirming that these products are directly connected to the peroxyl radical intermediate.

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ID Code: 71659
Item Type: Journal Article
Refereed: Yes
Keywords: cavity ringdown spectroscopy, organic peroxy-radicals, mass-spectrometry, photoelectron-spectroscopy, electronic-transition, molecule reactions, c-h, kinetics, thermochemistry, chemistry
DOI: 10.1021/jp9073398
ISSN: 1520-5215 (online ) 1089-5639 (print)
Divisions: Current > Schools > School of Chemistry, Physics & Mechanical Engineering
Current > QUT Faculties and Divisions > Science & Engineering Faculty
Copyright Owner: Copyright 2009 American Chemical Society
Deposited On: 19 May 2014 22:47
Last Modified: 30 May 2014 06:25

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