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Very low‐pressure pyrolysis (VLPP) of but‐1‐yne the heat of formation and stabilization energy of the propargyl radical
Author(s) -
King Keith D.
Publication year - 1978
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.550100603
Subject(s) - chemistry , propargyl , radical , arrhenius equation , pyrolysis , standard enthalpy of formation , activation energy , yield (engineering) , shock tube , decomposition , thermal decomposition , atmospheric temperature range , medicinal chemistry , photochemistry , thermodynamics , organic chemistry , shock wave , catalysis , physics
The unimolecular decomposition of but‐1‐yne has been investigated over the temperature range of 1052° – 1152°K using the technique of very low‐pressure pyrolysis (VLPP). The primary process is CC bond fission yielding methyl and propargyl radicals. Application of RRKM theory shows that the experimental rate constants are consistent with the highpressure Arrhenius parameters given by\documentclass{article}\pagestyle{empty}\begin{document}$$ \log k(\sec ^{- 1}) = (1.55 \pm 0.3) - (74.2 \pm 2.0)/\theta $$\end{document}where θ = 2.303 RT kcal/mol. The parameters are in good agreement with estimates based on shock‐tube studies. The activation energy, combined with thermochemical data, leads to DH °[HCCCH 2 CH 3 ] = 76.0, Δ H f ° (HCCĊCH 2, g ) = 81.4, and DH ° [HCCCH 2 H] = 89.2, all in kcal/mol at 300°K. The stabilization energy of the propargyl radical SE ° (HCCĊCH 2 ) has been found to be 8.8 kcal/mol. Recent result for the shock‐tube pyrolysis of some alkynes have been analyzed and shown to yield values for the heat of formation and stabilization energy of the propargyl radical in excellent agreement with the present work. From a consideration of all results it is recommended that Δ H f,300 ° (HCCĊCH 2, g ) = 81.5±1.0, DH 300 ° [HCCCH 2 H] = 89.3 ± 1.0, and SE ° (HCCĊCH 2 ) = 8.7±1.0 kcal/mol.