Kinetics Database Resources
Title: Radical-molecule reactions HCO/HOC + C2H2: mechanistic study
Journal: J. Phys. Chem. A
Page(s): 11941 - 11955
Comments: No rate constants reported. Only energetics.
The energetics of the reactions of HCO and HOC with C2H2 (ethyne) were calculated using ab initio CCSD(T)/6-311G(2d,p) method. 150 molecular species, intermediates, and transition states are presented in paper, along with many, many pages of structures and energetics. However, most of the intermediates and transition states are irrrelevant since they are 40-50 kcal/mol above the lowest energy pathways, and involve highly strained cyclic structures and carbenes.
It is unclear why all these calculations were done since very few are relevant.
The lowest energy pathways are unsurprisingly HCO or HOC addition to C2H2, followed by H atom migration from the weak RC(O)-H bond to the C=CH* site, and then facile CO elimination. HCO + HC#CH -> HCO-CH=CH* -> CH2=CH-CO* -> CH2=CH* + CO
The barrier to addtion of HCO is about 11 kcal/mol with heat of reaction exothermic by 17 kcal/mol. The barrier to H atom migration is about 14 kcal/mol (rel to reactants) with a overall heat of reaction of about 38 kcal/mol exothermic. Elimination of CO is about 17 kcal/mol endothermic with a small reverse barrier to addtion.
Reaction of HOC with C2H2 is essentially barrierless with a heat of reaction of 24 kcal/mol exothermic.
C2H2 + HCO → CO + C2H3
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