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Notes: The life times of chemically activated alcohols have been determined using the high-pressure unimolecular rate parameters for thermal decomposition of alcohols from shocktube studies and RRKM calculations. They are compared with literature numbers (from insertion of 0(1D) into hydrocarbons). It is suggested that in some cases singlet oxygen carries excess energy into the hydrocarbon. The consequences of such an assumption are explored and discrepancies with previously published conclusions discussed.

Notes: 4-Methylhexyne-1, 5-methylhexyne-1, hexyne-1, and 6-methylheptyne-2 have been decomposed in comparative-rate single-pulse shock-tube experiments. Rate expressions for the initial decomposition reactions at 1100°K and from 2 to 6 atm pressure are \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}s {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + s{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{15.9} \exp (- 35,000/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm allene} + n{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{12.9} \exp (- 28,000/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + i{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{16.1} \exp (- 36,700/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}i {\rm C}_{\rm 4} {\rm H}_{\rm 9} \to {\rm allene} + i{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{2.3} \exp (- 27,500/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}n {\rm C}_{\rm 3} {\rm H}_{\rm 7} \to {\rm HC} \equiv {\rm CCH}_{\rm 2} \cdot + n{\rm C}_{\rm 3} {\rm H}_{\rm 7} \cdot) = 10^{15.9} \exp (- 36,300/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm HC} \equiv {\rm CCH}_{{\rm 2}^{{\rm -}}}n {\rm C}_{\rm 3} {\rm H}_{\rm 7} \to {\rm allene} + n{\rm C}_{\rm 3} {\rm H}_{\rm 6}) = 10^{12.7} \exp (- 28,400/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm CH}_3 {\rm C} \equiv {\rm CCH}_{2^{-}}i {\rm C}_4 {\rm H}_9 \to {\rm CH}_3 {\rm C}) \equiv {\rm CCH}_{\rm 2} \cdot + i{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot) = 10^{16.2} \exp (- 36,800/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm CH}_3 {\rm C} \equiv {\rm CCH}_{2^{-}}i {\rm C}_4 {\rm H}_9 \to 1,2-butadiene + i{\rm C}_{\rm 4} {\rm H}_{\rm 8}) = 10^{12.3} \exp (- 28,700/T)\sec ^{- 1} $$\end{document} In combination with previous results, rate expressions for propargyl C—C bond cleavage are related to that for the alkanes by the expression \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm B} (alkyne) = \frac{1}{{3 \pm 1.5}}\exp (+ 4.25/T)k_{\rm B} (alkane) $$\end{document} These results yield a propargyl resonance energy of D(nC3H7-H) - D(C3H3-H) = 36 ± 2 kJ, in excellent agreement with a previous shock-tube study. They also lead to D(CH3C≡CCH2-H) - D(C3H3-H) = 0.6 ± 3 kJ, D(sC4H9-H) - D(iC3H7-H) = 0 ± 3 kJ, D(iC4H9-H) - D(nC3H7-H) = 2 ± 3 kJ, and D(nC3H7-H) - D(iC3H7-H) = 13.9 ± 3 kJ (all values are for 300°K). The systematics of the molecular decomposition process are explored.

Notes: 1,1,1-Trifluoroethane has been decomposed in comparative rate single-pulse shock-tube experiments. The rate expression for elimination at ca. 2.5 bar and in the temperature range of 1050 to 1200 K has been found to be\documentclass{article}\pagestyle{empty}\begin{document}$ \it k\rm (CF_{3}\joinrel{\relbar\!\!\relbar}CH_{3}\relbar\!\!\rightarrow HF+CF_{2}=CH_{2})=7.0\times 10^{14}\ exp(-37260/T)s^{-1} $\end{document}The experimental conditions appear to be such that the unimolecular reaction is at the beginning of the fall-off region and we find that for step sizes down between 500 and 1000 cm-1 the high-pressure rate expression is in the range\documentclass{article}\pagestyle{empty}\begin{document}$ \it k\rm (CF_{3}\joinrel{\relbar\!\!\relbar}CH_{3}\relbar\!\!\rightarrow HF+CF_{2}=CH_{2})=2.0\times 10^{15}\ exp(-38300/T)\ to\ 4\ \times\ 10^{15}\ exp(-39000/T)s^{-1} $\end{document}where the smaller rate parameters refer to the larger step size down. The results are compared with those from an earlier study and the anomalously high A-factor is noted. It is suggested that the existing rate expressions for the fluorinated ethanes may need to be reevaluated. © 1998 John Wiley & Sons, Inc., Int J Chem Kinet: 30: 621-628, 1998

Notes: Dilute mixtures of 4-methyl-l-pentyne have been pyrolyzed in a single-pulse shock tube. The decomposition process involves bond breaking: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm HC} \equiv {\rm C} - {\rm CH}_2 ({\rm i - C}_{\rm 3} {\rm H}_{\rm 7} )\stackrel{k_B}{\longrightarrow}{\rm HC} \equiv {\rm C} - {\rm CH}_2 \cdot ({\rm propynyl}) + {\rm i - C}_{\rm 3} {\rm H}_{\rm 7} \cdot $$\end{document} as well as a molecular reaction: \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm HC}\equiv {\rm C} - {\rm CH}_{\rm 2} ({\rm \rm i - C}_{\rm 3} {\rm H}_{\rm 7} )\stackrel{k_M}{\rightarrow}{\rm C}_{\rm 3} {\rm H}_4 ({\rm allene}) + {\rm C}_3 {\rm H}_6 . $$\end{document} The rate parameters are: \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\bf B} = 10^{15.56} \exp {\rm (} - 34,940/T){\rm (sec}^{ - {\rm 1}}) $$ $$\begin{array}{*{20}c} k_{\rm M} = 10^{13.1} \exp {\rm (} - {\rm 29,670/}T){\rm (sec}^{ - {\rm 1}})&{\rm 1100}^ \circ {\rm K, 1}{\rm .5} - 5{\rm atm}\end{array}$$\end{document} The heat of formation of propynyl radical is thus ΔHf300 = 338 kJ mol-1 (80.7 kcal mol-1)· This leads to a propynyl resonance energy of 40 kJ mol-1 (9.6 kcal mol-1).

Notes: A check of the data from comparative rate single-pulse shock tube experiments have been carried out through the use of a new standard reaction, the decyclization reaction of ethylcyclobutane. The rate expressions for cyclohexene and 2,2,3-trimethylbutane have been found to be \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} k({\rm C}_{\rm 6} {\rm H}_{{\rm 10}} \to 1,3 - {\rm C}_4 {\rm H}_6 + {\rm C}_2 {\rm H}_4 ) = 10^{15.3} \exp ( - 33,690/T)\sec ^{ - 1} ,950^ \circ - 1100^ \circ {\rm K,2} - {\rm 6atm} \\ k(t{\rm C}_4 {\rm H}_9 - {\rm iC}_3 {\rm H}_7 \to t{\rm C}_{\rm 4} {\rm H}_{\rm 9} \cdot + {\rm iC}_{\rm 3} {\rm H}_7 \cdot ) = 10^{16.5} {{\exp ( - 36,830} \mathord{\left/ {\vphantom {{\exp ( - 36,830} T}} \right. \kern-\nulldelimiterspace} T})\sec ^{ - 1} ,1000^ \circ - 1100^ \circ {\rm K,2} - {\rm 6atm} \\ \end{array} $$\end{document} in excellent agreement with previously published results. Most of the small discrepancy that does exist is apparently due to the differences between the present and earlier (decomposition of isopropyl bromide) "standard" reaction. For the latter process, the present study yields \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm iC}_{\rm 3} {\rm H}_7 {\rm Br} \to {\rm C}_{\rm 3} {\rm H}_6 + {\rm HBr}) \to 10^{13.73} {\rm exp(}{{ - 23,970} \mathord{\left/ {\vphantom {{ - 23,970} {T\sec ^{ - 1} ,800^ \circ - 1000^ \circ {\rm K,2} - {\rm 6}}}} \right. \kern-\nulldelimiterspace} {T\sec ^{ - 1} ,800^ \circ - 1000^ \circ {\rm K,2} - {\rm 6}}}{\rm atm)} $$\end{document} These results confirm the correctness of previously published comparative rate single-pulse shock tube experiments. They demonstrate once again that for the decomposition of paraffin hydrocarbons, calculated preexponential factors are at least an order of magnitude higher than the directly measured number and that the accepted value of the heat of formation of t-butyl radicals ΔHf300(tC4H9·) = 29 kJ (6.8 kcals) is at least 10 kJ too low. Finally, attention is called to recent studies on neopentane decomposition in flow and static systems which are in complete agreement with the present conclusions.

Notes: Tertiary-amyl amine has been decomposed in single-pulse shock-tube experiments. Rate expressions for several of the important primary steps are \documentclass{article}\pagestyle{empty}\begin{document}$$ k(t{\rm C}_5 {\rm H}_{11 - {\rm NH}_2} \to t{\rm C}_5 {\rm H}_{11}\!\!\cdot + {\rm NH}_2\cdot) = 10^{15.9} \exp (-39,700/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k({\rm C}_2 {\rm H}_5- {\rm C}({\rm CH}_3)_2{\rm NH}_2 \to {\rm C}_2 {\rm H}_5 \cdot + \cdot{\rm C}({\rm CH}_3)_2{\rm NH}_2) = 10^{16.5} \exp (- 38,500/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k(t{\rm C}_5 {\rm H}_{11} {\rm NH}_2 \to {\rm C}_5 {\rm H}_{10} + {\rm NH}_3) 〈10^{14.5} \exp (- 37,200/T)\sec ^{- 1} $$\end{document}This leads to D(CH3—H) - D(NH2—H) = -10.5 kJ and D[(CH3)3C—H] - D[(CH3)2NH2C—H] = + 6 kJ.The present and earlier comparative rate single-pulse shock-tube data when combined with high-pressure hydrazine decomposition results-(after correcting for fall off effects through RRKM calculations) gives \documentclass{article}\pagestyle{empty}\begin{document}$$ [k_r^2 (t{\rm C}_5 {\rm H}_{11} \cdot,{\rm NH}_2 \cdot)/k_r (t{\rm C}_5 {\rm H}_{11} \cdot,t{\rm C}_5 {\rm H}_{11} \cdot)k_r ({\rm NH}_2 \cdot,{\rm NH}_2 \cdot)]^{1/2} \sim 2\,{\rm at}\,1100^o {\rm K} $$\end{document} where kr(…) is the recombination rate involving the appropriate radicals. This suggests that in this context amino radical behavior is analogous to that of alkyl radicals. If this agreement is exact, then \documentclass{article}\pagestyle{empty}\begin{document}$$ k_\infty ({\rm N}_2 {\rm H}_4 \to 2{\rm NH}_2 \cdot) = 10^{16.25} \exp (- 32,300/T)\sec ^{- 1} $$\end{document} Rate expressions for the primary step in the decomposition of a variety of primary amines have been computed. In the case of benzyl amine where data exist the agreement is satisfactory. The following differences in bond energies have been estimated: \documentclass{article}\pagestyle{empty}\begin{document}$$ D(i{\rm C}_3 {\rm H}_7 {-\!-} {\rm H}) {-\!-} D[{\rm CH}_3 ({\rm NH}_2){\rm CH} {-\!-} {\rm H}] = 14.3\,{\rm kJ} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ D({\rm C}_2 {\rm H}_5 {-\!-} {\rm H}) - D({\rm NH}_2 {\rm CH}_2 {-\!-} {\rm H}) = 15.9\,{\rm kJ} $$\end{document}

Notes: Hexamethylethane has been decomposed in a flow system in the temperature range of 700-900 K. The mechanism involves carbon-carbon bond cleavage at the most highly substituted position and rapid formation of isobutene from the t-butyl radical. The rate expression is \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{*{20}c}{k({\rm (tC}_{\rm 4} {\rm H}_{\rm 9})_2 \to 2t{\rm C}_{\rm 4} {\rm H}_{\rm 9}.) = 10^{17.4} {\rm exp(} - 36,000/{\rm T)}} & {{\rm sec}^{ - 1}}\\\end{array} $$\end{document} and is completely consistent with deductions from radical buffer, shock-tube, and direct recombination studies. Of special importance is experimental evidence for large decreases of the A factor with increasing temperature and a high heat of formation for the t-butyl radical, ΔHf(tC4H9·)300 = 52.7 ± 6 kJ.

Notes: 5-Methyl-hexanone-2, 3-methyl-pentanone-2, and hexanone-2 have been decomposed in comparative rate single pulse shock tube experiments. The mechanism of decomposition involves the breaking of carbon-carbon bonds as well as molecular processes involving 6-center complexes. The following rate expressions at 1100 K have been obtained: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{rcl} k(3{\rm - methyl - pentanone - 2} \to {\rm CH}_{\rm 3} {\rm \dot CO} + {\rm sC}_4 {\rm H}_9 .) = 10^{16.4} \exp (- 38,300/T)/{\rm s} \\ k(5{\rm - methyl - hexanone - 2} \to {\rm CH}_{\rm 3} {\rm \dot CO} + {\rm iC}_4 {\rm H}_9 .) = 10^{16.6} \exp (- 40,600/T)/{\rm s} \\ k(5{\rm - methyl - hexanone - 2} \to {\rm CH}_{\rm 3} {\rm COCH}_{\rm 3} + {\rm iC}_4 {\rm H}_8) = 10^{12.56} \exp (- 31,600/T)/{\rm s} \\ k({\rm hexanone - 2} \to {\rm CH}_{\rm 3} {\rm COCH}_{\rm 3} + {\rm C}_3 {\rm H}_6) = 10^{13.28} \exp (- 32,400/T)/{\rm s} \\ \end{array} $$\end{document} These results lead to ΔHf(CH3ĊO) = - 13.8 kJ and ΔHf(CH3COCH2·) = - 12.6 kJ at 300 K. They are compared with existing literature values and some generalizations are made with regard to the stability of carbonyl compounds.

Notes: 2,4-Dimethylhexene-l has been decomposed in single-pulse shock tube experiments. Rate expressions for the initial reactions are \documentclass{article}\pagestyle{empty}\begin{document}$$ k(C_4 H_7 - S - C_4 H_9 \to C_4 H_7 .(isobutenyl) + s - C_4 H_9 .) = 10^{15.6} \exp (- 33,200/T)\sec ^{ - 1} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k(C_4 H_7 - S - C_4 H_8 \to _i C_4 H_8 + n - C_4 H_8 .) = 10^{12.5} \exp (- 26,900/T)\sec ^{ - 1} $$\end{document} sec-1 at 1.5-5 atm and 1050°K. This leads to ΔH°f300 (CH2 = C(CH3)CH2) = 124 kJ/mol, or an allylic resonance energy of 50 kJ/mol. Rate expressions for the decomposition of the appropriate olefins which yield isobutenyl radicals and methyl, ethyl, isopropyl, n-propyl, t-butyl, and t-amyl radicals, respectively, are presented. The rate expression for the decomposition of isobutenyl radical is \documentclass{article}\pagestyle{empty}\begin{document}$$ k{\rm (C}_{\rm 4} H_7 .(isobutenyl) \to C_3 H_4 (allene) + CH_3 .) = 10^{13.3} \exp (- 2,500/T)\sec ^{ - 1} $$\end{document} (at the beginning of the fall-off region). For the combination of isobutenyl and methyl radicals, the rate constant at 1020°K is \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k(C}_{\rm 4} H_7 .(isobutenyl) + CH_3 . \to 2 - methylbutene - 1) = 10^{10.3} 1./mol\sec $$\end{document} Combination of this number and the calculated rate expression for 2-methylbutene-1 decomposition gives SC4H7. (1100) = 470 J/mol °K. This yields \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k(C}H_3 + C_3 H_4 (allene) \to C_4 H_7 .(isobutenyl) = 10^{8.2} \exp (- 2,500/T)l./mol\sec $$\end{document} It is demonstrated that an upper limit for the rate of hydrogen abstraction by isobutenyl from toluene is \documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm k(C}_{\rm 4} H_7 . + \emptyset CH_3 \to iC_4 H_8 + \emptyset CH_2 .)\underline \le 10^{8.3} \exp (- 6,000/T)l./mol\sec $$\end{document}

Notes: 3,3-Dimethylbutanol-2 (3,3-DMB-ol-2) and 2,3-dimethylbutanol-2 (2,3-DMB-ol-2) have been decomposed in comparative-rate single-pulse shock-tube experiments. The mechanisms of the decompositions are The rate expressions are \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm B} (2,3{\rm - DBM - ol - 2}) = 10^{16.24} {\rm exp}(- 37,400/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm EP} (2,3{\rm - DBM - ol - 2}) = 10^{14.17} {\rm exp}(- 32,300/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm ET} (2,3{\rm - DBM - ol - 2}) = 10^{13.66} {\rm exp}(- 32,700/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm B} (3,3{\rm - DBM - ol - 2}) = 10^{16.33} {\rm exp}(- 37,500/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k_{\rm EP} (3,3{\rm - DBM - ol - 2}) = 10^{14.0} {\rm exp}(- 34,200/T)\sec ^{- 1}$$\end{document} They lead to D(iC3H7—H) - D((CH3)2(OH) C—H) = 8.3 kJ and D(C2H5—H) - D(CH3(OH) CH—H) = 24.2 kJ.These data, in conjunction with reasonable assumptions, give \documentclass{article}\pagestyle{empty}\begin{document}$$k(t{\rm C}_{\rm 4} {\rm H}_{\rm 9} {\rm OH} \to {\rm CH}_{\rm 3} \cdot + \cdot {\rm C(CH}_{\rm 3} {\rm)}_{\rm 2} {\rm OH}) = 10^{16.8} {\rm exp}(- 40,900/T)\sec ^{- 1} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k(i{\rm C}_{\rm 3} {\rm H}_{\rm 7} {\rm OH} \to {\rm CH}_{\rm 3} \cdot + \cdot {\rm CH(CH}_{\rm 3} {\rm)OH}) = 10^{16.5} {\rm exp}(- 41,100/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k(n{\rm C}_{\rm 3} {\rm H}_{\rm 7} {\rm OH} \to {\rm CH}_{\rm 3} \cdot + \cdot {\rm CH}_{\rm 2} {\rm CH}_{\rm 2} {\rm OH}) = 10^{16.2} {\rm exp}(- 41,100/T)\sec ^{- 1}$$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$k({\rm C}_{\rm 2} {\rm H}_{\rm 5} {\rm OH} \to {\rm CH}_{\rm 3} \cdot + \cdot {\rm CH}_{\rm 2} {\rm OH}) = 10^{16.4} {\rm exp}(- 42,500/T)\sec ^{- 1}$$\end{document}andThe rate expressions for the decomposition of 2,3-DMB-1 and 3,3-DMB-1 are \documentclass{article}\pagestyle{empty}\begin{document}$$ k(2,3{\rm - DMB - 1} \to {\rm CH}_3 \cdot + {\rm H}_2 {\rm C} = {\rm C}({\rm CH}_3 ) - \mathop {\mathop {\rm C}\limits^{\rm .} {\rm H}({\rm CH}_3 )) = 10^{16.0} \exp ( - 35,700/T)\sec ^{ - 1} } $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ k(3,3{\rm - DMB - 1} \to {\rm CH}_{\rm 3} \cdot + {\rm H}_2 {\rm C = CH} - \mathop {\rm C}\limits^{\rm .} ({\rm CH}_3 )_2 ) = 10^{16.2} \exp ( - 35,500/T)\sec ^{ - 1} $$\end{document}