摘要:
                                Photochemical nitrogen elimination from 1-(diazomethyl)-8-methylnaphthalene (2) yields acenaphthene (3) via the reactive intermediates (8-methyl-1-naphthyl)carbene (a) and 1,8-naphthoquinodimethane (b).  The triplet biradical b was observed by absorption spectroscopy at 77 K and by laser flash photolysis at room temperature.  The cyclization of triplet b to triplet 3 is forbidden by state symmetry.  Two pathways for the reaction b --> 3 have been identified:  (1) intersystem crossing to the singlet groud state is rate-determining in the thermal decay of b, and (2) an adiabatic reaction yielding 3 in the lowest excited triplet state was observed upon photolysis of triplet b at 77 K.  The carbene precursor of b was intercepted by methanol.  This resulted in a reduced yield of transient b in acetonitrile.  The trapping reaction did not obey a linear Stern-Volmer relationship.