Reaction Mechanism of CH + C₃H₆: A Theoretical Study

Abstract

A detailed theoretical study is performed at the B3LYP/6-311G(d,p) and G3B3 (single-point) levels as an attempt to explore the reaction mechanism of CH with C(3)H(6). It is shown that the barrierless association of CH with C(3)H(6) forms two energy-rich isomers CH(3)-cCHCHCH(2) (1), and CH(2)CH(2)CHCH(2) (4). Isomers 1 and 4 are predicted to undergo subsequent isomerization and dissociation steps leading to ten dissociation products P(1) (CH(3)-cCHCHCH + H), P(2) (CH(3)-cCCHCH(2) + H), P(3) (cCHCHCH(2) + CH(3)), P(4) (CH(3)CHCCH(2) + H), P(5) (cis-CH(2)CHCHCH(2) + H), P(6) (trans-CH(2)CHCHCH(2) + H), P(7) (C(2)H(4) + C(2)H(3)), P(8) (CH(3)CCH + CH(3)), P(9) (CH(3)CCCH(3) + H) and P(12) (CH(2)CCH(2) + CH(3)), which are thermodynamically and kinetically possible. Among these products, P(5), P(6), and P(7) may be the most favorable products with comparable yields; P(1), P(2), and P(3) may be the much less competitive products, followed by the almost negligible P(4), P(8), P(9), and P(12). Since the isomers and transition states involved in the CH + C(3)H(6) reaction all lie lower than the reactant, the title reaction is expected to be fast, which is consistent with the measured large rate constant in experiment. The present study may lead us to a deep understanding of the CH radical chemistry.

Product Branching Fractions of the CH + Propene Reaction from Synchrotron Photoionization Mass Spectrometry

“…propene limit is at +125 kcal/mol relative to 1-methylallyl. 16 The hydrogen in blue would originate from the CH radical in accord with the scheme in Figure 5. (not depicted in Figure 6) including allene + CH 3 34 that are not detected in our experiment.…”

“…At the photon energy resolution of this experiment, we are not able to distinguish cis/trans isomers. Other structural isomers of C 4 H 6 , for example cyclic species considered by Li et al 16 , correspond to considerably less exothermic product channels and are excluded as discussed below. For the purpose of fitting the m/z 54 photoionization spectrum to apportion individual contributions from the main product isomers, the absolute photoionization spectra of these butadiene and butyne species are required and are included as Supporting Information ( Figure S2).…”

“…16 This study considered two entrance pathways for this reaction: (i) cycloaddition and (ii) insertion (into a C-H σ-bond) (see Scheme 1). isomer-specific, product data are essential to understand the mechanisms of this reaction and to test the computational predictions.…”

“…16 This study considered two entrance pathways for this reaction: (i) cycloaddition and (ii) insertion (into a C-H σ-bond) (see Scheme 1). Each entrance pathway leads to distinct intermediate C 4 H 7 isomers.…”

Theoretical insights into the reaction mechanisms between 2,3,7,8-tetrachlorodibenzofuran and the methylidyne radical

“…Its extreme reactivity arises from the presence of one singly occupied and one vacant nonbonding molecular orbital localized on the carbon atom. 37 Therefore, CH radical can react with most species ranging from small alkanes, [28][29][30][31] alkene, 28,[32][33][34][35][36][37][38] alkyne, 28,33,[37][38][39] pyrrole, 41 acrolein 42 to large polycyclic aromatic hydrocarbons like anthracene (C 14 H 10 ), 43 providing an alternative way to synthesize long-chain or ring-expanded hydrocarbons and complex organic molecules. For example, CH radical can react with pyrrole to produce the ring expansion product pyridine, 41 where CH radical can be readily prepared experimentally via the photolysis of bromoform at room temperature.…”