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The Decomposition and Isomerization of 5-Methylhex-1-yl Radical



Iftikhar A. Awan, William S. McGivern, Wing Tsang, Jeffrey A. Manion


The decomposition and isomerization reactions of the 5-methylhex-1-yl radical (1-5MeH) have been studied at temperatures of 889 K to 1064 K and pressures of 1.6 bar to 2.2 bar using the single pulse shock tube technique. The radical of interest was generated by shock heating dilute mixtures of 5-methylhexyl iodide to break the weak C-I bond, and the kinetics and reaction mechanism deduced on the basis of the olefin cracking pattern observed by gas chromatographic analysis of the products. In order of decreasing molar yields, alkene products from 1-5MeH decomposition are ethene, isobutene, propene, 3-methylbut-1-ene, but-1-ene, E/Z-hex-2-ene, 4-methylpent-1-ene, and hex-1-ene. The first three products account for almost 90% of the carbon balance. The mechanism involves reversible intramolecular H-transfer reactions that lead to the formation of the radicals 5-methylhex-5-yl (5-5MeH), 5-methylhex-2-yl (2-5MeH), 5-methylhex-4-yl (4-5MeH), 5-methylhex-6-yl (6-5MeH), and 5-methylhex-3-yl (3-5MeH). Competitive with isomerization reactions are decompositions by beta C-C bond fission. The main product forming radical is 5-5MeH, which is formed by intramolecular abstraction of the lone tertiary H in the radical. This reaction is deduced to be a factor of 4.0 ± 0.7 faster on a per hydrogen basis than the analogous abstraction of a secondary hydrogen in 1-hexyl radical. The estimated uncertainty corresponds to one standard deviation.
Journal of Physical Chemistry A


kinetics, pyrolysis, shock-tube, unimolecular, combustion


Awan, I. , McGivern, W. , Tsang, W. and Manion, J. (2010), The Decomposition and Isomerization of 5-Methylhex-1-yl Radical, Journal of Physical Chemistry A, [online], (Accessed April 14, 2024)
Created July 8, 2010, Updated October 12, 2021