High temperature behavior of alternant and nonalternant polycyclic aromatic hydrocarbons

Three different flash vacuum pyrolysis (FVP) set-ups were employed for the study of the thermal behavior of alternant and nonalternant polyclic aromatic hydrocarbons (PAH). The 1,2-switch of carbon atoms in the thermal automerizations of PAH, previously observed in benzene, pyrene and benz[a]anthracene, has been additionally observed for [1-C-13]anthracene, [6-C-13]benzo[c]phenanthrene and [1-C-13]- and [4-C-13]phenanthrenes at temperatures between 900 and 1100 degrees C. Bay region PAH (chrysene, benz[a]anthracene, phenanthrene, picene, perylene, benzo[ghi]perylene, benzo[e]pyrene, and benz[a,c]-anthracene) were discovered to undergo an intriguing transformation when heated at 1100 degrees C; the transformation is believed to be triggered by cyclodehydrogenation across the bay region. Thermal formation of five-membered rings was used to synthesize a series of new nonalternant hydrocarbons. When the thermal closure of a five-membered ring is energetically unfavorable, migration of an ethynyl group from one benzene ring to another along the edge of a PAH (e.g. anthracene) can take place. (C) 2000 Published by Elsevier Science B.V.