PHOTOCHEMISTRY OF MATRIX-ISOLATED DIAZOETHANE AND METHYLDIAZIRINE - ETHYLIDENE TRAPPING

Photolysis of matrix-isolated diazoethane (1a) at 8 K produces mainly ethene (4a), along with a small amount of 3-methyldiazirine (2a). ESR experiments employing a variety of irradiation conditions and matrix media (Ar, N2, Xe) show that triplet ethylidene (3T) is not an observable photoproduct. Similar experiments fail to reveal direct evidence for either singlet or triplet ethylidene by IR or UV-vis spectroscopy. Photolysis of nascent 3-methyldiazirine (2a) also fails to yield ethylidene. Deuterium substitution produces no detectable change in the chemistry. In carbon monoxide-doped matrices, photolysis of 1 generates 3-methyldiazirine (2) and ethene (4) as well as a small amount of methylketene (5). The most plausible interpretation of these results postulates that (i) trapping of incipient singlet- ethylidene (3S) by CO competes with the facile hydrogen migration and (ii) intersystem crossing to the triplet does not compete with hydrogen migration.