Kinetic Isotope Effects as Probes of the Mechanism of Reaction of 1-Naphthylcarbene with Cyclohexane and Toluene

Article abstract of DOI:10.1021/ja00250a027

The rates of reaction of 1-naphthylcarbene (1-NC) in hydrocarbon solution have been measured with excimer laser flash photolysis of 1-naphthyldiazomethane.The kinetic data were obtained by monitoring the growth of the 1-naphthylmethyl radical (1-NCH) at 370 nm.The observed kinetic deuterium isotope effect for the reaction of 1-NC with cyclohexane (cyclohexane-d₁₂) in 2,2,4-trimethylpentane (k_H/k_D = 1,32 +/- 0.17) and the high CH insertion to H-atom abstraction product ratio are consistent with largely singlet reactivity for 1-NC.In toluene, where addition to the aromatic ring is favored over hydrogen atom abstraction, the measured inverse isotope effect (k_H/k_D = 0.52 +/- 0.05) also argues for predominantly singlet reactivity and a small singlet-triplet energy gap.The Arrhenius activation parameters measured for the reaction of NC with cyclohexane and toluene were E_act = 2.43 +/- 0.19 kcal/mol, log (A, s^-1) = 7.70 +/- 0.15 and E_act = 1.93 +/- 0.38 kcal/mol, log (A, s^-1) = 7.28 +/- 0.30, respectively.