Reaction of phenoxy radical with nitric oxide

The associationof C 6 H 5 O with NO was studied with the cavity‐ring‐down method by directly monitoring the decay of C 6 H 5 O in the presence of varying, excess amounts of NO. The biomolecular rate constant determined in the temperature range 297‐373 K can be effectively rate constant determined in the temperature range 297–373 K can be effectively represented by k 1 = 10   − 12 · 12 ± 0.24   e(194±185)/rcm 3 molecule −1 with a negative activation energy of 0.8 kcal mol −1 (1 kcal = 4.184 kJ). In order to understand better the mechanism of the reaction, ab initio molecular orbital calculations were also carried out at the MP4(SDQ)/6‐31G* level of theory using the HF optimized geometries. The molecular structues and energetics of five C 6 H 5 N 1 O 2 isomers were calculated. Among them, the most likely and stable association product, phenyl nitrite (C 4 H 5 ONO), was found to be 17 kal mol −1 below the reactants, C 6 H 5 O + NO. Combining the measured rate constant and the calculated equilibrium constant for the association reaction, C 6 H 5 O + NO = C 6 H 5 ONO the rate constant for the unimolecular decomposition of C 6 H 5 ONO was obtained as k −1 = 4.6 × 10 15 E −8580/T s −1 . The relatively large frequency factor suggests that a loose transition state was involved in the reaction, akin to those of its alkyl analogs (RONO, R CH 3 , C 2 H 5 , etc.).