Flash vacuum thermolysis of acenaphtho[1,2-a]acenaphthylene, fluoranthene,benzo[k]- and benzo[j]fluoranthene - Homolytic scission of carbon-carbon single bonds of internally fused cyclopenta moieties at T >= 1100 degrees C

Flash vacuum thermolysis (FVT, 1000 degrees C greater than or equal to T gr eater than or equal to 1200 degrees C) of acenaphtho[1,2-a]acenaphthylene ( 3, C22H12) gave the C22H12 cyclopenta-fused polycyclic aromatic hydrocarbon (CP-PAH) acenaphtho[1,2-e]acenaphthylene (4), cyclopenta[cd]perylene (5) a nd cyclopenta[def]benzo[hi]chrysene (6). Whereas the formation of 4 is expl ained by a ring contraction/ring expansion rearrangement of 3, the identifi cation of 5 and 6 suggests that 3 also undergoes homolytic scission of a fi ve-membered ring's carbon-carbon single bond furnishing the transient dirad ical intermediate 7. Ring closure of 7 to form 8 after rotation around the carbon-carbon single bond of the intact five-membered ring followed by hydr ogen shifts will give 6. The latter can rearrange subsequently into 5 by ri ng contraction/ring expansion. The structural assignment of 4 and 5 was sup ported by independent FVT of 6,12-bis(1-chloroethenyl)chrysene (14) and 3-( 1-chloroethenyl)perylene (23), respectively. FVT of 14 (900-1200 degrees C) gave in a consecutive process 6,12-bis(ethynyl)chrysene (15), 9-ethynylben z[j]acephenanthrylene (16) and bis(cyclopenta[hi,qr])chrysene (17). Althoug h at T greater than or equal to 900 degrees C 17 selectively rearranges int o 4 by ring contraction/ring expansion, at 1200 degrees C the latter is con verted into 5 presumably via a diradical intermediate obtained by homolytic scission of a single carbon-carbon bond of a five-membered ring. FVT of 23 gave in situ 3-ethynylperylene (25), which at 1000 degrees C is nearly qua ntitatively converted into 5. The propensity of internal cyclopenta moietie s to undergo homolytic scission of a five-membered ring's carbon-carbon sin gle bond was corroborated by independent FVT of benzo[k]- (11) and benzo[j] fluoranthene (12). Previously unknown thermal pathways to important (CP)-PA H combustion effluents are disclosed at T greater than or equal to 1000 deg rees C.