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

Abstract

The novel C₂₀H₁₂ cyclopenta-fused polycyclic aromatic hydrocarbon benz[l]acephenanthrylene (2) and its isomer benz[ j]acephenanthrylene (3) have been obtained by flash vacuum thermolysis of 2-(1-chloroethenyl)benzo[c]phenanthrene (6) and 6-(1-chloroethenyl)chrysene (7), respectively. At T ⩾ 900 °C 2 and T ⩾ 1000 °C 3 rearrange selectively to the abundant combustion effluent benzo[j]fluoranthene (1). No evidence for the presence of the related rearrangement products benz[l]aceanthrylene (12) and benz[j]aceanthrylene (13), respectively, is found. Semi-empirical AM1 calculations provide a rationalization for these observations; the conversion of 2 and 3 into 1, instead of 12 and 13, respectively, via consecutive ring-contraction–ring-expansion processes and vice versa is favoured.

References

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