New Approach to the Detection of Short-Lived Radical Intermediates

We report a new general method for trapping short-lived radicals, based on a homolytic substitution reaction S(H)2'. This departure from conventional radical trapping by addition or radical-radical cross-coupling results in high sensitivity, detailed structural information, and general applicability of the new approach. The radical traps in this method are terminal alkenes possessing a nitroxide leaving group (e.g., allyl-TEMPO deriva-tives). The trapping process thus yields stable products which can be stored and subsequently analyzed by mass spectrometry (MS) supported by well-established techniques such as isotope exchange, tandem MS, and high-performance liquid chromatography-MS. The new method was applied to a range of model radical reactions in both liquid and gas phases including a photoredox-catalyzed thiol-ene reaction and alkene ozonolysis. An unprecedented range of radical intermediates was observed in complex reaction mixtures, offering new mechanistic insights. Gas-phase radicals can be detected at concentrations relevant to atmospheric chemistry.

Automated summary

The new method for trapping short-lived radicals utilizes a homolytic substitution reaction S(H)2', resulting in high sensitivity, detailed structural information, and general applicability. By using radical traps in the form of terminal alkenes with a nitroxide leaving group, stable products are generated for subsequent analysis, offering new mechanistic insights into a range of model radical reactions. Gas-phase radicals can also be detected at concentrations relevant to atmospheric chemistry.