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Laser Flash Photolysis and Computational Study of Singlet Phenylnitrene

Journal of the American Chemical Society1999Vol. 121(6), pp. 1202–1207

Citations Over TimeTop 10% of 1999 papers

Nina P. Gritsan, Zhendong Zhu, Christopher M. Hadad, Matthew S. Platz

Abstract

Laser flash photolysis (LFP, Nd:YAG laser, 35 ps, 266 nm, 10 mJ) of phenyl azide (PA) releases open-shell singlet phenylnitrene (1PN). 1PN has a sharp absorption band at 350 nm and a very weak absorption band at 540 nm. These bands are assigned as nz−ny and a mixture of 52% π−nx and 28% nx−π* transitions, respectively, on the basis of CASSCF and CASPT2 calculations. A CASPT2 calculation of the spectrum of triplet phenylnitrene (3PN) is in very good agreement with the experimental spectrum. A sharp absorption band of 3PN at 308 nm and a broad, structured band at 370 nm are assigned as nz−ny and π−π transitions on the basis of CASSCF and CASPT2 calculations. The low intensity, long wavelength band of 3PN tailing to 500 nm is assigned as a mixture of π−nx, nx−π* transitions. The decay of 1PN in pentane was measured as a function of temperature to obtain observed rate constants of disappearance, kobs. The rate constant kobs is equal to kR + kISC, where kR is the absolute rate constant of rearrangement of 1PN to benzazirine and kISC is the absolute rate constant of intersystem crossing to the lower energy triplet state (3PN). When it is assumed that kISC is independent of temperature, kobs can be dissected, and absolute values of kR and kISC can be deduced. For 1PN, kISC = 3.2 ± 0.3 × 106 s-1 and the Arrhenius parameters for kR are found to be Ea = 5.6 ± 0.3 kcal mol-1 and A = 1013.1±0.3 s-1.

Citations Over TimeTop 10% of 1999 papers

Abstract

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