Reaction of vinyl radical with oxygen: A matrix isolation infrared spectroscopic and theoretical study

Abstract

The reaction of vinyl radical with molecular oxygen in solid argon has been studied using matrix isolation infrared absorption spectroscopy. The vinyl radical was produced through high frequency discharge of ethylene. The vinyl radical reacted with oxygen spontaneously on annealing to form the vinylperoxy radical C(2)H(3)OO with the O-O bond in a trans position relative to the C-C bond, which is characterized by O-O stretching and out-of-plane CH(2) bending vibrations at 1140.7 and 875.5 cm(-1). The vinylperoxy radical underwent visible photon-induced dissociation to the CH(2)OH(CO) complex or CH(2)OH+CO, which has never been considered in previous studies. The CH(2)OH(CO) product was predicted to be more thermodynamically accessible than the previously reported major HCO+H(2)CO channel, and is most likely produced by hydrogen atom transfer from the first-formed H(2)CO-HCO pair in solid argon.

The O‐Directed Free Radical Hydrostannation of Propargyloxy Dialkyl Acetylenes with Ph3SnH/cat. Et3B. A Refutal of the Stannylvinyl Cation Mechanism

“…Significantly, as well, von Sonntag found these vinyl radical additions were irreversible as was found to be the case by Carpenter et al, a decade later. So, these combined observations would all appear to strongly counter the errant mechanistic claims of Organ, Oderinde and Froese about how vinyl radicals typically react with triplet O 2 ,…”

“… Carpenter's matrix isolation IR spectroscopic and theoretical study of how vinyl radical reacts with 3 O 2 . Carpenter observed both the vinyl peroxyradical 332 and the vinyl radical 325 at the IR absorptions indicated …”

“…This alkene self‐cleavage process is the primary reaction pathway followed by peroxyvinyl radicals at ambient temperature and pressure, and the 3‐ exo‐trig mode of ring‐closure is of lower activation energy than the corresponding 4‐ endo‐trig cyclisation to the dioxetanyl radical 334 , which is associated with much higher steric strain. In terms of defining how vinyl radical itself reacts with triplet O 2 , the work of the Carpenter team is unambiguous, this group having assigned the 1140 cm −1 and 875.5 cm −1 absorptions to the vinyl peroxy radical 332 via infrared absorption spectroscopy, having generated the radical in an Argon matrix at 4 K that was subsequently annealed at 25 K.…”

“…Significantly, they conclusively showed that vinyl radicals react with 3 O 2 to give vinylperoxy radicals that then oxidatively cleave. In this instance, the fluorenone 343 was actually isolated by Lodder, proving that vinylic radicals typically undergo alkene oxidative cleavage, by a mechanism that we now know to be analogous to that proposed later in 2005 by Carpenter . This work further refutes the Scheme mechanistic suggestion for the role of O 2 in O‐directed free radical hydrostannations of alkyl‐ and aryl‐ acetylenes, it proving that vinyl radicals react with O 2 by a totally different radical addition pathway that subsequently involves alkene cleavage.…”

Effect of Methyl Group Substitution on the Kinetics of Vinyl Radical + O2 Reaction

“…Majority of the previous studies of vinyl-type radicals with molecular oxygen have been confined to the kinetics of reaction CH2CH + O2. [13][14][15][16][17][18][19][20] However, in our recent work we studied the kinetics of methyl-vinyl radicals with molecular oxygen and observed that substituting the α-hydrogen of vinyl radical with a methyl group increased reactivity towards O2, whereas substituting a β-hydrogen with a methyl group decreased reactivity towards O2. 21 In this work, we have further investigated the reactivity trends by measuring the kinetics of 2,2-dimethylvinyl and 1,2,2-trimethylvinyl radicals with molecular oxygen as function of temperature.…”