Kinetics and mechanisms of charge-transfer nitration. Part 2. Time-resolved spectral evolution of the ipso adducts from 1,4-dimethylnaphthalene cation radical

Abstract

The transient intermediates accompanying the charge-transfer excitation of the 1,4-dimethylnaphthalene (DMN) complex with either the N-nitropyridinium or tetranitromethane acceptor are identified as the cation radical DMN^+˙ paired with NO₂ and either pyridine or trinitromethanide. Time-resolved (ps and ns–µs) spectroscopy allows the temporal evolution of these triads of reactive intermediates to the ipso adducts 1 and 2 to be followed in detail and the mechanistic relationship to nuclear and sidechain (methyl) nitration is delineated. The role of added pyridine bases in the promotion of sidechain nitration is discussed.