文摘
Product and mechanistic studies were performed for the reaction of aromatic distonic peroxyl radical cations 4-PyrOO鈥? and 3-PyrOO鈥? with phenylacetylene (7) in the gas phase using mass spectrometric and computational techniques. PyrOO鈥? was generated through reaction of the respective distonic aryl radical cation Pyr鈥? with O2 in the ion source of the mass spectrometer. For the reaction involving the more electrophilic 4-PyrOO鈥?, a rate coefficient of k1 = (2.2 卤 0.6) 脳 10鈥?0 cm3 molecule鈥? s鈥? was determined at 298 K, while a value of k2 = (8.2 卤 2.1) 脳 10鈥?1 cm3 molecule鈥? s鈥? was obtained for the reaction involving the less electrophilic 3-PyrOO鈥?. This highlights the role of polar effects in these reactions, which are likely of high relevance for processes in combustions and atmospheric transformations. The mechanism was studied by computational methods, which showed that radical addition occurs exclusively at the less substituted alkyne site to give the distonic vinyl radical cation 8. The latter undergoes a series of subsequent rearrangements/fragmentations that are similar for both isomeric PyrOO鈥?. 纬-Fragmentation in 8 leads to the distonic aryloxyl radical cation PyrO鈥? and a singlet carbene 10. The product association complex [PyrO鈥? 鈥?10] is the starting point for two important subsequent reactions, e.g., (i) rapid hydrogen transfer to form ketenyl radical 11 and the closed-shell species PyrOH+, and (ii) oxygen transfer from PyrO鈥? to 10 that leads to 伪-keto aldehyde 13 and Pyr鈥?, followed by hydrogen abstraction to give acyl radical 14 and PyrH+. Additional major products are the closed-shell aromatic carbonyl compounds 20 and 30 that result from multistep rearrangements in vinyl radical 8, which are terminated by homolytic bond scission and release of neutral acyl radicals.