RATES OF DECARBOXYLATION OF ACYLOXY RADICALS FORMED IN THE PHOTOCLEAVAGE OF SUBSTITUTED 1-NAPHTHYLMETHYL ALKANOATES

Rates of decarboxylation (k(CO2)R) have been estimated for the acyloxy radicals 7a-f formed in the photolysis of substituted 1-naphthylmethyl alkanoates 6a-f. These rates are based on a proposed mechanism involving initial carbon-oxygen homolytic bond cleavage from the excited singlet state. The products are formed by two competing pathways: electron transfer in the radical pair to give an ion pair and decarboxylation. Measured product yields along with an estimate of the electron-transfer rate (k(ET)) allow calculation of k(CO2)R as a function of R. The values obtained are the following (R, k (10(9) s-1)): CH3, < 1.3; CH3CH2, 2.0; (CH3)2CH, 6.5; (CH3)3C, 11; PhCH2, 5.0; PhCH2CH2, 2.3.