Skip to main content

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

Journal Article


Abstract


  • 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 ((C6H10)-C-center dot-CO2-) 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 ((OO)-O-center dot-C6H10-CO2-), providing the first direct observation of a cyclohexylperoxyl radical, and (ii) elimination of HO2 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 HO2 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 HO2 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 (OO)-O-center dot-C6H10-CO2- by collision induced disassociation also results in the loss Of HO2 center dot and HO center dot radicals confirming that these products are directly connected to the peroxyl radical intermediate.

UOW Authors


  •   Kirk, Benjamin B. (external author)
  •   Harman, David G. (external author)
  •   Blanksby, Stephen J. (external author)

Publication Date


  • 2010

Citation


  • Kirk, B. B., Harman, D. & Blanksby, S. (2010). Direct observation of the gas phase reaction of the cyclohexyl radical with dioxygen using a distonic radical ion approach. The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory, 114 (3), 1446-1456.

Scopus Eid


  • 2-s2.0-77249116312

Ro Metadata Url


  • http://ro.uow.edu.au/scipapers/5110

Has Global Citation Frequency


Number Of Pages


  • 10

Start Page


  • 1446

End Page


  • 1456

Volume


  • 114

Issue


  • 3

Abstract


  • 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 ((C6H10)-C-center dot-CO2-) 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 ((OO)-O-center dot-C6H10-CO2-), providing the first direct observation of a cyclohexylperoxyl radical, and (ii) elimination of HO2 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 HO2 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 HO2 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 (OO)-O-center dot-C6H10-CO2- by collision induced disassociation also results in the loss Of HO2 center dot and HO center dot radicals confirming that these products are directly connected to the peroxyl radical intermediate.

UOW Authors


  •   Kirk, Benjamin B. (external author)
  •   Harman, David G. (external author)
  •   Blanksby, Stephen J. (external author)

Publication Date


  • 2010

Citation


  • Kirk, B. B., Harman, D. & Blanksby, S. (2010). Direct observation of the gas phase reaction of the cyclohexyl radical with dioxygen using a distonic radical ion approach. The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment and General Theory, 114 (3), 1446-1456.

Scopus Eid


  • 2-s2.0-77249116312

Ro Metadata Url


  • http://ro.uow.edu.au/scipapers/5110

Has Global Citation Frequency


Number Of Pages


  • 10

Start Page


  • 1446

End Page


  • 1456

Volume


  • 114

Issue


  • 3