THE NUCLEOPHILICITY OF SUPEROXIDE TOWARDS DIFFERENT ALKYL-HALIDES ESTIMATED FROM KINETIC MEASUREMENTS

Values of the rate constant k(sub) are measured for the substitution reaction between superoxide O2-. and the alkyl halides butyl chloride, 2-butyl chloride, benzyl chloride, ethyl bromide, butyl bromide, 2-butyl bromide, neopentyl bromide, benzyl bromide, (1-bromo-2,2-dimethylpropyl)benzene and 1-iodoadamantane. These rate constants are compared with the expected rate constant k(ET) for the electron transfer reaction between the same alkyl halides and an aromatic anion radical A-. with the same standard oxidation potential as O2-.. The k(sub)/k(ET) ratios show that the mechanism of the substitution reaction may shift from S(N)2-like to ET-like on changes in the steric hindrance and the acceptor ability of the alkyl halide. The influence on k(sub)/k(ET) of the difference in self-exchange reorganization energy lambda(0) between O2-./O2 and A-./A is discussed.