Journal
CHEMPHYSCHEM
Volume 20, Issue 11, Pages 1437-1447Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.201900052
Keywords
ab initio calculations; gas-phase chemistry; hydrogen abstraction-acetylene addition (HACA); mass spectrometry; polycyclic aromatic hydrocarbons
Funding
- US Department of Energy, Basic Energy Sciences [DE-FG02-03ER15411, DE-FG02-04ER15570]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy through the Gas Phase Chemical Physics program in the Chemical Sciences Division [DE-AC02-05CH11231]
- Ministry of Higher Education and Science of the Russian Federation [14.Y26.31.0020]
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The reactions of the indenyl radicals with acetylene (C2H2) and vinylacetylene (C4H4) is studied in a hot chemical reactor coupled to synchrotron based vacuum ultraviolet ionization mass spectrometry. These experimental results are combined with theory to reveal that the resonantly stabilized and thermodynamically most stable 1-indenyl radical (C9H7.) is always formed in the pyrolysis of 1-, 2-, 6-, and 7-bromoindenes at 1500 K. The 1-indenyl radical reacts with acetylene yielding 1-ethynylindene plus atomic hydrogen, rather than adding a second acetylene molecule and leading to ring closure and formation of fluorene as observed in other reaction mechanisms such as the hydrogen abstraction acetylene addition or hydrogen abstraction vinylacetylene addition pathways. While this reaction mechanism is analogous to the bimolecular reaction between the phenyl radical (C6H5.) and acetylene forming phenylacetylene (C6H5CCH), the 1-indenyl+acetylene -> 1-ethynylindene+hydrogen reaction is highly endoergic (114 kJ mol(-1)) and slow, contrary to the exoergic (-38 kJ mol(-1)) and faster phenyl+acetylene -> phenylacetylene+hydrogen reaction. In a similar manner, no ring closure leading to fluorene formation was observed in the reaction of 1-indenyl radical with vinylacetylene. These experimental results are explained through rate constant calculations based on theoretically derived potential energy surfaces.
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