Publication Details

Prendergast, M., Cooper, P. A., Kirk, B. B., da Silva, G., Blanksby, S. J. and Trevitt, A. J. (2013). Hydroxyl radical formation in the gas phase oxidation of distonic 2-methylphenyl radical cations. Physical Chemistry Chemical Physics, 15 (47), 20577-20584.


The reactions of distonic 4-(N,N,N-trimethylammonium)-2-methylphenyl and 5-(N,N,N-trimethylammonium)-2-methylphenyl radical cations (m/z 149) with O 2 are studied in the gas phase using ion-trap mass spectrometry. Photodissociation (PD) of halogenated precursors gives rise to the target distonic charge-tagged methylphenyl radical whereas collision-induced dissociation (CID) is found to produce unreactive radical ions. The PD generated distonic radicals, however, react rapidly with O2 to form [M + O2]•+ and [M + O2 - OH]•+ ions, detected at m/z 181 and m/z 164, respectively. Quantum chemical calculations using G3SX(MP3) and M06-2X theories are deployed to examine key decomposition pathways of the 5-(N,N,N-trimethylammonium)-2-methylphenylperoxyl radical and rationalise the observed product ions. The prevailing product mechanism involves a 1,5-H shift in the peroxyl radical forming a QOOH-type intermediate that subsequently eliminates •OH to yield charge-tagged 2-quinone methide. Our study suggests that the analogous process should occur for the neutral methylphenyl + O2 reaction, thus serving as a plausible source of •OH radicals in combustion environments.

Grant Number

ARC/DP0986738, ARC/DP130100862