Substituent effects on the lifetimes and reactivities of arylnitrenium ions studied by laser flash photolysis and photothermal beam deflection

Photolysis of 5-substituted-N-tert-butyl-3-methylanthranilium produces transient N-tert-butyl-(2-acetyl-4-substituted) phenylnitrenium ions. This is confirmed by identification of the stable products, transient absorption experiments, and photothermal beam deflection experiments. Analysis of the stable photoproducts shows that the major decay pathway for these species is addition of nucleophiles to the aromatic ring. The kinetics of the these reactions were examined with the goal of determining how various ring substituents affect arylnitrenium ion stability. Rate constants measured for the 4-phenyl and 4-methoxy derivatives are compared with those from previous work. It is shown that a 4-phenyl group stabilizes the nitrenium ion to approximately the same extent as a 4-methoxy group. Both of these substituents stabilize the arylnitrenium ions considerably more than 4-halogens or a 4-methyl group. Time resolved photothermal beam deflection experiments were applied to the 4-cyano and 4-unsubstituted derivatives, which gave no transient absorption spectra. The latter two compounds are shown to have lifetimes of less than 100 ns.