Reaction of phenoxy radical with nitric oxide

The associationof C₆H₅O with NO was studied with the cavity‐ring‐down method by directly monitoring the decay of C₆H₅O 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 k₁ = 10 − 12 · 12 ± 0.24 e (194±185)/r cm³ 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 C₆H₅N₁O₂ isomers were calculated. Among them, the most likely and stable association product, phenyl nitrite (C₄H₅ONO), was found to be 17 kal mol⁻¹ below the reactants, C₆H₅O + NO. Combining the measured rate constant and the calculated equilibrium constant for the association reaction, C₆H₅O + NO = C₆H₅ONO the rate constant for the unimolecular decomposition of C₆H₅ONO was obtained as k₋₁ = 4.6 × 10¹⁵E^−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  CH₃, C₂H₅, etc.).