ABSOLUTE RATE CONSTANTS OF CONSUMPTION OF ISOMERS OF AROMATIC NITROSO OXIDES 4-R-C6H4CH2-C6H4NOO, R = OH, NHCOCH3

The decay kinetics of cis- and trans-isomers of aromatic nitroso oxides 4-R-C6H4CH2-C6H4NOO (R = OH, NHCOCH3) was studied by pulse photolysis and electron spectrophotometry at 279 – 343 K in acetonitrile solutions. The effective rate constants kcis and ktrans, as well as their activation parameters, were determined. Aromatic nitroso oxides ArNOO were generated by photolysis of the corresponding azides ArN3 in aerated ace tonitrile solutions. It was found that lgkcis (s-1) = (11.7 ± 0.5) – (64.2 ± 2.6)/ for R = OH and (13.1 ± 0.1) – (72.4 ± 0.1)/ for R = NHCOCH3,  = 2.303RT kJ/mol. Accordingly, for trans-isomers it was obtained: lgktrans (s-1) = (9.9 ± 1.5) – (60.3 ± 6.3)/ and (10.7 ± 0.3) – (65.1 ± 0.1)/. In the M06L/6-311+G(d,p) + IEFPCM approximation, the difference in Gibbs free energies of cis-trans isomers was determined and used to calculate the conformational equilibrium constant. Using this value and the analytical solution of the system of kinetic differential equations, the absolute rate constants (s-1) of the elementary stages of the ArNOO consump tion were calculated for both nitroso oxides: the rate constant of trans-cis isomerization is 0.22 (R = OH), 0.20 (R = NHCOCH3); the rate constant of the reverse cis-trans transition is 0.17 (R = OH), 0.14 (R = NHCOCH3); and the rate constant of irreversible ortho-cyclization of the cis-isomer ArNOO is 2.67 (R = OH), 2.41 (R = NHCOCH3), T = 298 K. The Arrhenius parameters of the absolute rate constants were determined.