title: Using distonic radical ions to probe the chemistry of key combustion intermediates: the case of the benzoxyl radical anion.
abstract: The benzoxyl radical is a key intermediate in the combustion of toluene and other aromatic hydrocarbons, yet relatively little experimental work has been performed on this species. Here, a combination of electrospray ionization (ESI), multistage mass spectrometry experiments, and density functional theory (DFT) calculations are used to examine the formation and fragmentation of a benzoxyl (benzyloxyl) distonic radical anion. Excited 4-carboxylatobenzoxyl radical anions were produced via two methods: (1) collision induced dissociation (CID) of the nitrate ester 4-(nitrooxymethyl)benzoate, (-)O2CC6H4CH2ONO2, and (2) reaction of ozone with the 4-carboxylatobenzyl radical anion, (-)O2CC6H4CH2(•). In neither case was the stabilized (-)O2CC6H4CH2O(•) radical anion intermediate detected. Instead, dissociation products at m/z 121 and 149 were observed. These products are attributed to benzaldehyde (O2(-)CC6H4CHO) and benzene ((-)O2CC6H5) products from respective loss of H and HCO radicals in the vibrationally excited benzoxyl intermediate. In no experiments was a product at m/z 120 (i.e., (-)O2CC6H4(•)) detected, corresponding to absence of the commonly assumed phenyl radical + CH2=O channel. The results reported suggest that distonic ions are useful surrogates for reactive intermediates formed in combustion chemistry.
authors.affiliation: School of Chemistry, The University of Melbourne, Melbourne, VIC, Australia.
authors.forename: Cong
authors.initials: C
authors.lastname: Li
authors.forename: Adrian K Y
authors.initials: AK
authors.lastname: Lam
authors.forename: George N
authors.initials: GN
authors.lastname: Khairallah
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: White
authors.forename: Richard A J
authors.initials: RA
authors.lastname: O'Hair
authors.forename: Gabriel
authors.initials: G
authors.lastname: da Silva
mesh_terms: D000838:Anions / Q000737:chemistry; D001565:Benzoates / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006358:Hot Temperature; D008956:Models, Chemical; D008958:Models, Molecular; D010084:Oxidation-Reduction; D053719:Tandem Mass Spectrometry
chemical_list: D000838:Anions; D001565:Benzoates; D005609:Free Radicals; C013409:benzoyl chloride