Spectroscopic characterization of 2-naphthylcarbene

Abstract

The 308 nm excimer laser flash photolysis of 2-naphthyldiazomethane produces triplet 2-naphthylcarbene (λ max = 362 nm) which decays with the observed pseudo-first-order rate constants (k exptl) of 5.54 ± 0.03 × 10 6; 3.33 ± 0.4 × 10 6; 1.64±0.02 × 10 7; and 3.05±0.4 × 10 6 s -1 in n-pentane, 2,2,4-trimethylpentane (2,2,4-TMP), benzene and Freon 113 respectively. In hydrocarbon solvents the observed decay of triplet 2-naphthylcarbene is correlated with the pseudo-first-order growth of the 2-naphthylmethyl radical (λ max = 378 nm). Direct kinetic measurements of the reaction of triplet 2-naphthylcarbene in 2,2,4-TMP with cyclohexane, styrene, methanol and carbon tetrachloride yielded bimolecular quenching rate constants of 1.48 ± 0.04 × 10 6;4.33 ± 0.1 × 10 7;7.25 ± 0.5 × 10 6; and 3.35 ± 0.07 × 10 6M -1S -1. It is also found that 2-naphthylcarbene reacts with acetonitrile (k q = 5.28 ± 0.1 × 10 5 M -1 s -1) to form a nitrile ylide intermediate with a λ max = 372 nm. These results are interpreted in terms of a rapid singlet-triplet 2-naphthylcarbene equilibrium.