%0 Journal Article %A Sarobe, Martin %A Jenneskens, Leonardus W. %A Steggink, Ralph G. B. %A Visser, Tom %D 1999 %T Origin of Pyrene under High Temperature Conditions in the Gas Phase. The Pivotal Role of Phenanthrene %U https://acs.figshare.com/articles/journal_contribution/Origin_of_Pyrene_under_High_Temperature_Conditions_in_the_Gas_Phase_The_Pivotal_Role_of_Phenanthrene/3716493 %R 10.1021/jo982030e.s001 %2 https://acs.figshare.com/ndownloader/files/5808057 %K PAH %K flash vacuum thermolysis %K ratio %K FVT %K pyrene %K insertion %K formation %K carbene %K C 2 addition %K High Temperature Conditions %K chloroethenyl %K ethynyl substituents %K Phenanthrene %X 4-Ethynylphenanthrene (15), and the latent precursors for 2-ethynyl- (18) and 3-ethynylphenanthrene (19), viz., 2-(1-chloroethenyl)- (16) and 3-(1-chloroethenyl)phenanthrene (17), respectively, have been subjected to flash vacuum thermolysis (FVT). Whereas at 800 °C 15 is quantitatively converted into pyrene (1), 16 and 17 only give 18 and 19, respectively. Both 18 and 19 contain redundant ethynyl substituents, i.e., after ethynyl−ethylidene carbene equilibration neither five- nor six-membered ring formation can occur by carbene C−H insertion. At T ≥ 1000 °C 16 and 17 gave pyrolysates containing the same set of 11 (non)-alternant polycyclic aromatic hydrocarbons (PAH), albeit in a different ratio. The different product ratio suggests that redundant ethynyl substituents migrate along the phenanthrene periphery presumably via transient cyclobuta-PAH intermediates toward positions suitable for either five- or six-membered ring formation by carbene C−H insertion. The results provide an explanation for the ubiquitous formation of pyrene (1), acephenanthrylene (9), and fluoranthene (3) during (incomplete) combustion. Phenanthrene (2) appears to be a point of divergence in PAH growth by C2 addition. %I ACS Publications