posted on 2021-10-21, 17:39authored byAnatoliy
A. Nikolayev, Valeriy N. Azyazov, Ralf I. Kaiser, Alexander M. Mebel
Ab
initio CCSD(T)-F12/cc-pVTZ-f12//ωB97X-D/6-311G(d,p)
+ ZPE[ωB97X-D/6-311G(d,p)] calculations were carried out to
unravel the area of the C5H7 potential energy
surface accessed by the reaction of the methylidyne radical with 1-butyne.
The results were utilized in Rice–Ramsperger–Kassel–Marcus
calculations of the product branching ratios at the zero pressure
limit. The preferable reaction mechanism has been shown to involve
(nearly) instantaneous decomposition of the initial reaction adducts,
whose structures are controlled by the isomeric form of the C4H6 reactant. If CH adds to the triple CC
bond in the entrance reaction channel, the reaction is predicted to
predominantly form the methylenecyclopropene + methyl (CH3) and cyclopropenylidene + ethyl (C2H5) products
roughly in a 2:1 ratio. CH insertion into a C–H bond in the
methyl group of 1-butyne is anticipated to preferentially form ethylene
+ propargyl (C3H3) by the C–C bond β-scission
in the initial complex, whereas CH insertion into C–H of the
CH2 group would predominantly produce vinylacetylene +
methyl (CH3) also by the C–C bond β-scission
in the adduct. The barrierless and highly exoergic CH + 1-butyne reaction,
facile in cold molecular clouds, is not likely to lead to the carbon
skeleton molecular growth but generates C4H4 isomers methylenecyclopropene, vinylacetylene, and 1,2,3-butatriene
and smaller C2 and C3 hydrocarbons such as methyl,
ethyl, and propargyl radicals, ethylene, and cyclopropenylidene.