Absolute Kinetics of Aminium Radical Reactions with Olefins in Acetonitrile Solution1

Photolysis of N-nitrosamines in acidic acetonitrile produces aminium radical cations via protonation of the initially-formed aminyl radicals. The kinetics of these species can be monitored by transient UV spectroscopy via their absorption band which is found at ca. 300 nm in the case of the piperidinium radical, for example. By measuring the aminium radicals' lifetimes as a function of the concentration of added olefin, absolute values for the bimolecular rate constants for the addition reactions were obtained. In the case of the piperidinium radical, these rate constants varied from 1 × 108 s-1 upon the phenyl substitution at the olefinic terminus.