Isomeric forms of arylnitroso oxides: Electronic spectra and reactivity

The electronic spectra were measured and the kinetics of unimolecular decomposition of the isomeric forms (cis and trans) of phenylnitroso oxide, (4-methylphenyl)nitroso oxide, (4-nitropenyl)nitroso oxide, (4-bromophenyl)nitroso oxide, 4-(N,N-dimethylamino)phenylnitroso oxide, and (4-methoxyphenyl)nitroso oxide in acetonitrile, benzene, and n-hexane was studied using flash photolysis. In all of the nitroso oxides except for 4-(N,N-dimethylamino)phenyinitroso oxide, the cis form absorbed in a shorter wavelength region and was more labile than the trans form. The difference between the reactivity of the two species increased on going from n-hexane to acetonitrile. The temperature dependence of reaction rate constants was studied for both of the isomeric forms. Unlike the trans isomer, the cis isomer almost did not react with tetramethylethylene.