RED LIGHT-INDUCED REACTION OF NO2 WITH 2,3-DIMETHYL-2-BUTENE IN A LOW-TEMPERATURE ARGON MATRIX

Red light-induced oxygen atom transfer from NO2 to 2,3-dimethyl-2-butene has been investigated in a low-temperature argon matrix. The IR spectra of a reaction intermediate indentified as an alkyl nitrite radical and two final products, tetramethyloxirane and 3,3-dimethyl-2-butanone (pinacolone), were observed. From analysis of the absorbance growth of the IR bands, first-order rate constants were determined by least-square fitting. Based on these results and those of our earlier works on NO2 photoreactions with other alkenes, a reaction mechanism is proposed that involves oxygen atom transfer from NO2 to the C=C bond Of 2,3-dimethyl-2-butene to give a short-lived singlet oxirane biradical. Alkyl nitrite radical is produced by a recombination of the transient biradical with NO trapped in the cage of the matrix. Tetramethyloxirane and pinacolone emerge from secondary photolysis of the trapped alkyl nitrite radical.