Spectral and kinetic measurements on a series of persistent iminoxyl radicals

A series of new iminoxyl radicals, Et3C(C=NO·)Bu-tert (1), tert-C5H11(C=NO·) Bu-tert (2), (tert-C5H11)2C=NO· (3), Et3C(C=NO·)Ph (4), PhCH2CMe2(C=NO·)Bu-tert (5), PhCMe2(C=NO·)Bu-tert (6) and Me2CH(C=NO·)C5H11-tert (7), was characterized by EPR and in some cases visible spectra and decay kinetics in solution. Isolation of 1H and 3-tert-butyl-4,4-diethyl-5-methyl-4,5-dihydro-5-isoxazolol (9) among the decomposition products of 1 was consistent with a previously unrecognized mode of iminoxyl reaction in which the initial step is an internal β-H abstraction. Molecular orbital calculations on H2C=NO· indicate a C–N–O angle of about 140° and a 10 kcal mol−1 barrier to inversion. Rate constants for the reaction of tert-Bu2C=NO· (8) with a series of olefins were measured. © 1997 John Wiley & Sons, Ltd.