Unimolecular Reaction Properties for the Long‐Chain Alkenyl Radicals

Abstract

Although alkenyl radicals are important intermediates involved in both alkanes and alkenes combustion, previous kinetic studies on them are very limited, especially for the long‐chain alkenyl radicals. To deeply investigate unimolecular reaction activities of long‐chain alkenyl radicals, a series of octenyl (C8H15) radicals were chosen to study the reaction kinetics of three typical types of reactions (i.e., intramolecular radical addition, internal H‐migration, and bond dissociation) in this work. The CBS‐QB3 method was used to build potential energy surfaces for these reactions, and the transition state theory was applied to obtain the high‐pressure limit rate constants. Some general rules are observed from our systematic calculations in respect of structure–activity relationships.

Structure‐dependence in initial decomposition of trans‐1,2‐dimethylcyclohexyl isomers: Kinetic exploration and conformational analysis

“…Due to the substituent effect, βCC2 in M2Cee R is more favorable than its βCC1. Moreover, the rates for all CH dissociations are lower than those for CC β‐scissions, which brings into correspondence with the former conclusion [41]. The rate coefficients for 1‐ethylcyclohexyl and 1‐methylcyclohexyl radicals are larger than the relevant ones in present work, resulting from their low barriers shown in Figure 6C.…”

“…However, their rate coefficients F I G U R E 1 2 High pressure limit rate coefficients of β-scissions for (1-methyl-cyclohex-2-yl)-methyl (M1) in trans-configurations demonstrate a greater slope with the increasing temperature since the entropy effect becomes dominate. It agree well with the findings for alkenyl [41] and cyclic alkyl radicals [4,7]. Noticed that all βCC2 paths are the most favorable with bond cleavage between two side chains, which is correspondence with the experimental results for 1,2-DMCH and 1,3-DMCH [11,19].…”

“…For each initial decomposition type for trans-1,2DMCH radicals, the rate coefficients for the most favored path are displayed in Figure 16. It aims to gain insight into their competitions over 300-2500 K. One thing should be mentioned here that the subsequent reactions for alkenyl radicals, produced by the ring-opening reactions of trans-1,2DMCH radicals, are difficult to investigate, since they are complex enough for typically F I G U R E 1 5 High pressure limit rate coefficients of β-scissions for 3,4-dimethyl-cyclohex-1-yl (M4) in trans-configurations including three different classes of reactions reported by our previous studies [41,42]. As such, although the kinetics by thoroughly considering all subsequent reactions would be better to unravel their competitions, it requires much more efforts and is beyond the scope of this article.…”

Experimental and modeling study of 1-octene jet-stirred reactor oxidation

“…This radical can subsequently eliminate an H atom either by reaction with O2 or by β-scission to form 3-ethylcyclohexene or 4-ethylcyclohexene. Such formation pathways were investigated in recent theoretical studies [40,41]. However, the current mechanism lacks of low-temperature reactions related to ethyl-cyclohexane and ethyl-cyclohexenes, for which very few papers can be found in the literature.…”

“…• The rate constants for the decomposition by C−C bond breaking of C8 alkenyl and allylic radicals were adopted from the recent theoretical work of Bian et al [40].…”