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Issue 31, 2010
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Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

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Abstract

The reaction of the ground state methylidyne radical CH (X2Π) with pyrrole (C4H5N) has been studied in a slow flow tube reactor using Multiplexed Photoionization Mass Spectrometry coupled to quasi-continuous tunable VUV synchrotron radiation at room temperature (295 K) and 363 K, at 4 Torr (533 Pa). Laser photolysis of bromoform (CHBr3) at 248 nm (KrF excimer laser) is used to produce CH radicals that are free to react with pyrrole molecules in the gaseous mixture. A signal at m/z = 79 (C5H5N) is identified as the product of the reaction and resolved from 79Br atoms, and the result is consistent with CH addition to pyrrole followed by H-elimination. The photoionization efficiency curve unambiguously identifies m/z = 79 as pyridine. With deuterated methylidyne radicals (CD), the product mass peak is shifted by +1 mass unit, consistent with the formation of C5H4DN and identified as deuterated pyridine (d-pyridine). Within detection limits, there is no evidence that the addition intermediate complex undergoes hydrogen scrambling. The results are consistent with a reaction mechanism that proceeds via the direct CH (CD) cycloaddition or insertion into the five-member pyrrole ring, giving rise to ring expansion, followed by H atom elimination from the nitrogen atom in the intermediate to form the resonance stabilized pyridine (d-pyridine) molecule. Implications to interstellar chemistry and planetary atmospheres, in particular Titan, as well as gas-phase combustion processes, are discussed.

Graphical abstract: Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

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Publication details

The article was received on 01 Feb 2010, accepted on 08 Apr 2010 and first published on 12 May 2010


Article type: Paper
DOI: 10.1039/C002135K
Citation: Phys. Chem. Chem. Phys., 2010,12, 8750-8758
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    Direct detection of pyridine formation by the reaction of CH (CD) with pyrrole: a ring expansion reaction

    S. Soorkia, C. A. Taatjes, D. L. Osborn, T. M. Selby, A. J. Trevitt, K. R. Wilson and S. R. Leone, Phys. Chem. Chem. Phys., 2010, 12, 8750
    DOI: 10.1039/C002135K

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