HIGH-TEMPERATURE GAS-PHASE SYNTHESES OF C20H12 CYCLOPENTA-FUSED POLYCYCLIC AROMATIC-HYDROCARBONS - BENZ[L]ACEPHENANTHRYLENE AND BENZ[J]ACEPHENANTHRYLENE AND THEIR SELECTIVE REARRANGEMENT TO BENZO[J]FLUORANTHENE

The novel C20H12 cyclopenta-fused polycyclic aromatic hydrocarbon benz [l]acephenanthrylene (2) and its isomer benz[j]acephenanthrylene (3) h ave been obtained by hash vacuum thermolysis of 2-(1-chloroethenyl)ben zo[c]phenanthrene (6) and 6-(1-chloroethenyl)chrysene (7), respectivel y. At T greater than or equal to 900 degrees C 2 and T greater than or equal to 1000 degrees C 3 rearrange selectively to the abundant combu stion effluent benzo[j]fluoranthene (1). No evidence for the presence of the related rearrangement products benz[l]aceanthrylene (12) and be nz[j]aceanthrylene (13), respectively, is found. Semi-empirical AM1 ca lculations provide a rationalization for these observations; the conve rsion of 2 and 3 into 1, instead of 12 and 13, respectively, via conse cutive ring-contraction-ring-expansion processes and vice versa is fav oured.