Thermal decomposition of 3,4‐dimethylpentene‐1, 2,3,3‐trimethylpentane, 3,3‐dimethylpentane, and isobutylbenzene in a single pulse shock tube

Several hydrocarbons have been pyrolyzed in a single pulse shock tube. Rate parameters for the main bond breaking step have been found to be\documentclass{article}\pagestyle{empty}\begin{document}$$ k\left\{{{\rm iC}_3 {\rm H}_7 {-\!-} {\rm CH}\left({{\rm CH}_3} \right){\rm CH} {\raise1pt\hbox{$\Relbar \kern-4pt{\Relbar}$}} {\rm CH}_2 \longrightarrow {\rm iC}_3 {\rm H}_7 \cdot + \cdot {\rm CH}\left({{\rm CH}_3} \right){\rm CH} {\raise1pt\hbox{$\Relbar \kern-4pt{\Relbar}$}} {\rm CH}_2} \right\} = 10^{15.70} \exp \left({{{- 32,500} \mathord{\left/ {\vphantom {{- 32,500} T}} \right. \kern-\nulldelimiterspace} T}} \right)\sec ^{- 1} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k\left\{{{\rm iC}_3 {\rm H}_7 {-\!-} {\rm C}\left({{\rm CH}_3} \right)_2 {\rm C}_2 {\rm H}_5 \longrightarrow {\rm iC}_3 {\rm H}_7 \cdot + \cdot {\rm C}\left({{\rm CH}_3} \right)_2 {\rm C}_2 {\rm H}_5} \right\} = 10^{16.15} \exp \left({{{- 35,900} \mathord{\left/ {\vphantom {{- 35,900} T}} \right. \kern-\nulldelimiterspace} T}} \right)\sec ^{- 1} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k\left\{{{\rm C}_2 {\rm H}_5 {-\!-} {\rm C}\left({{\rm CH}_3} \right)_2 {\rm C}_2 {\rm H}_5 \longrightarrow {\rm C}_2 {\rm H}_5 \cdot + \cdot {\rm C}\left({{\rm CH}_3} \right)_2 {\rm C}_2 {\rm H}_5} \right\} = 10^{16.57} \exp \left({{{- 38,800} \mathord{\left/ {\vphantom {{- 38,800} T}} \right. \kern-\nulldelimiterspace} T}} \right)\sec ^{- 1} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k\left\{{{\rm iC}_3 {\rm H}_7 {-\!-} {\rm CH}_2 {\rm C}_6 {\rm H}_5 \longrightarrow {\rm iC}_3 {\rm H}_7 \cdot + \cdot {\rm CH}_2 {\rm C}_6 {\rm H}_5} \right\} = 10^{15.23} \exp \left({{{- 34,800} \mathord{\left/ {\vphantom {{- 34,800} T}} \right. \kern-\nulldelimiterspace} T}} \right)\sec ^{- 1} $$\end{document}In combination with similar studies carried out earlier and through application of the well‐established experimental rule ( k   r 2 (AB)/ k r (AA) k r (BB)) 1/2 ∼ 2 where A and B are radicals and the rate constants are for the combination of these radicals, rate parameters for the thermal decomposition of all the hydrocarbons formed from any pair of the following radicals: methyl, ethyl, isopropyl, t ‐butyl, t ‐amyl, allyl, methylallyl, and benzyl have been calculated. The available calculated and experimental values of the decomposition rate constants are in excellent agreement. It appears that, with the possible exception of reactions involving the ejection of methyl radicals, the frequency factors per bond are nearly constant, depending only upon the type of carbon–carbon bond that is being broken. These values are all lower than those expected from the radical recombination rates. Heats of formation of ethyl, t ‐amyl, benzyl, methylallyl, n‐propyl, s ‐butyl, isobutyl, neopentyl, and 3‐pentyl radicals have been derived. Rate parameters for the decomposition of some simple ketones and ethers have also been estimated.