Investigation of the Photolysis of Phosphites by Time-Resolved Electron Spin Resonance
| Autor: | Igor V. Koptyug, Srinivasan Ganapathy, Nicholas J. Turro, Naresh D. Ghatlia, Gregory W. Sluggett, Wesley G. Bentrude |
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| Rok vydání: | 1995 |
| Předmět: | |
| Zdroj: | Journal of the American Chemical Society. 117:9486-9491 |
| ISSN: | 1520-5126 0002-7863 |
| Popis: | The photochemistry of benzyl dimethyl phosphite (BDMPI), p-acetylbenzyl dimethyl phosphite (ABDPI) and 1-naphthylmethyl dimethyl phosphite (NMDPI) has been investigated by continuous wave time-resolved electron spin resonance (ESR) and Fourier transform time-resolved ESR techniques. The analysis of the detected ESR signals and their polarization patterns and temporal evolution elucidates the nature of the radical intermediates and the reaction pathway leading to their formation. No ESR signals were detected upon direct photolysis of BDMPI and NMDPI, consistent with a concerted reaction mechanism or predominant formation of a singlet radical pair. In sharp contrast to this, both p-acetylbenzyl and dimethoxyphosphonyl radicals have been detected upon direct photolysis of ABDPI in solution. The E*/A polarization patterns of the two radicals and their temporal evolution are consistent with the triplet reaction pathway. This is further confirmed by the triplet-sensitized photolysis of NMDPI, which yields the dimethoxyphosphonyl radical with the same E*/A polarization pattern. To make the analysis of spin polarization complete, the zero-field splitting parameters and relative population rates of the triplet sublevels of the molecular triplets of ABDPI and TMDPO ((2,4,6-trimethylbenzoyl)diphenylphosphine oxide) have been determined. These results in combination with product studies show that the direct photolysis of ABDPI proceeds via a triplet precursor to a significant extent. |
| Databáze: | OpenAIRE |
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