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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 °C
Author(s) -
Sarobe Martin,
Kwint Huibert C.,
Fleer Theun,
Havenith Remco W. A.,
Jenneskens Leonardus W.,
Vlietstra Edward J.,
van Lenthe Joop H.,
Wesseling Jolanda
Publication year - 1999
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199905)1999:5<1191::aid-ejoc1191>3.0.co;2-w
Subject(s) - chemistry , chrysene , bond cleavage , homolysis , fluoranthene , acenaphthylene , photochemistry , medicinal chemistry , stereochemistry , anthracene , organic chemistry , pyrene , radical , catalysis
Flash vacuum thermolysis (FVT, 1000 °C ≥ T ≥ 1200 °C) of acenaphtho[1,2‐ a ]acenaphthylene ( 3 , C 22 H 12 ) gave the C 22 H 12 cyclopenta‐fused polycyclic aromatic hydrocarbon (CP‐PAH) acenaphtho[1,2‐ e ]acenaphthylene ( 4 ), cyclopenta[ cd ]perylene ( 5 ) and cyclopenta[ def ]benzo[ hi ]chrysene ( 6 ). Whereas the formation of 4 is explained by a ring contraction/ring expansion rearrangement of 3 , the identification of 5 and 6 suggests that 3 also undergoes homolytic scission of a five‐membered ring's Carbon‐Carbon single bond furnishing the transient diradical 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 hydrogen shifts will give 6 . The latter can rearrange subsequently into 5 by ring contraction/ring expansion. The structural assignment of 4 and 5 was supported by independent FVT of 6,12‐bis(1‐chloroethenyl)chrysene ( 14 ) and 3‐(1‐chloroethenyl)perylene ( 23 ), respectively. FVT of 14 (900–1200 °C) gave in a consecutive process 6,12‐bis(ethynyl)chrysene ( 15 ), 9‐ethynylbenz[ j ]acephenanthrylene ( 16 ) and bis(cyclopenta[ hi,qr ])chrysene ( 17 ). Although at T ≥ 900 °C 17 selectively rearranges into 4 by ring contraction/ring expansion, at 1200 °C the latter is converted 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 °C is nearly quantitatively converted into 5 . The propensity of internal cyclopenta moieties to undergo homolytic scission of a five‐membered ring′s Carbon‐Carbon single bond was corroborated by independent FVT of benzo[ k ]‐ ( 11 ) and benzo[ j ]fluoranthene ( 12 ). Previously unknown thermal pathways to important (CP)‐PAH combustion effluents are disclosed at T ≥ 1000 °C.