B American Society for Mass Spectrometry, 2013 DOI: 10.1007/s13361-013-0596-y J. Am. Soc. Mass Spectrom. (2013) 24:493Y501 FOCUS: DISTONIC IONS: RESEARCH ARTICLE Using Distonic Radical Ions to Probe the Chemistry of Key Combustion Intermediates: The Case of the Benzoxyl Radical Anion Cong Li, 1,2,3,4 Adrian K. Y. Lam, 1,2,3,4 George N. Khairallah, 1,2,3 Jonathan M. White, 1,2 Richard A. J. O’Hair, 1,2,3 Gabriel da Silva 4 1 School of Chemistry, The University of Melbourne, Melbourne, VIC, Australia 2 Bio21 Institute of Molecular Science and Biotechnology, The University of Melbourne, Melbourne, VIC, Australia 3 ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, The University of Melbourne, Melbourne, VIC, 3010, Australia 4 Department of Chemical and Biomolecular Engineering, The University of Melbourne, Melbourne, VIC, Australia 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, – O 2 CC 6 H 4 CH 2 ONO 2 , and (2) reaction of ozone with the 4-carboxylatobenzyl radical anion, – O 2 CC 6 H 4 CH 2 • . In neither case was the stabilized – O 2 CC 6 H 4 CH 2 O • radical anion intermediate detected. Instead, dissociation products at m/z 121 and 149 were observed. These products are attributed to benzaldehyde (O 2 - CC 6 H 4 CHO) and benzene ( – O 2 CC 6 H 5 ) 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., – O 2 CC 6 H 4 • ) detected, corresponding to absence of the commonly assumed phenyl radical + CH 2 0O channel. The results reported suggest that distonic ions are useful surrogates for reactive intermediates formed in combustion chemistry. Key words: Distonic radical anions, Tandem mass spectrometry, DFT calculations, Toluene, Combustion Received: 30 October 2012/Revised: 20 February 2013/Accepted: 20 February 2013/Published online: 20 March 2013 Introduction M ost of the world’s energy is produced by the combustion of hydrocarbons, predominantly in the form of liquid transportation fuels and coal for electricity generation. The US Department of Energy has identified that advancements in engine and fuel technology have the potential to improve internal combustion engine efficiency by 25 % to 50 %, and that the overarching grand challenge in transport fuel usage is the development of predictive combustion models to help realize these efficiency gains [1]. These models require an elementary understanding of the complex reaction pathways involved in hydrocarbon oxida- tion, proceeding via reactive free radicals that can be difficult to observe using conventional experimental tech- niques. This has resulted in efforts to develop new experimental techniques to study radical reactions [2, 3] as well as an increased number of theoretical investigations. An approach that we have adopted to better understand the gas-phase chemistry of organic radical intermediates thought to be involved in combustion is to generate related charged radicals, in which the charge acts as a spectator and “handle” to allow ion trap mass spectrometry based analysis of product channels. Thus, we recently used the aromatic distonic N- methyl-pyridinium-4-yl radical cation to model the reaction of the phenyl radical with 2-butyne (CH 3 C ≡ CCH 3 )[4], a process involved in polycyclic aromatic hydrocarbon (PAH) formation. This distonic radical ion approach has also been used in the past Electronic supplementary material The online version of this article (doi:10.1007/s13361-013-0596-y) contains supplementary material, which is available to authorized users. Correspondence to: Richard A. J. O’Hair; e-mail: rohair@unimelb.edu.au