Theoretical Study of the Reaction of Hydrogen Atoms with Three Pentene Isomers: 2-Methyl-1-butene, 2-Methyl-2-butene, and 3-Methyl-1-butene

Abstract

This paper presents a comprehensive potential energy surface (PES) for hydrogen atom addition to and abstraction from 2methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene and the subsequent ß-scission and H atom transfer reactions. Thermochemical parameters for species on the C ̇5H 11 potential energy surface (PES) were calculated as a function of temperature (298−2000 K), using a series of isodesmic reactions to determine the formation enthalpies. High-pressure limiting and pressure-dependent rate constants were calculated using Rice−Ramsperger−Kassel−Marcus theory with a onedimensional master equation. A number of studies have highlighted the fact that C 5 intermediate species play a role in polyaromatic hydrocarbon formation and that a fuel's chemical structure can be key in understanding the intermediate species formed during fuel decomposition. Rate constant recommendations for both H ̇atom addition to, and H-atom abstraction by H ̇atoms from, linear and branched alkenes have subsequently been proposed by incorporating our earlier work on 1-and 2-pentene, and these can be used in mechanisms of larger alkenes for which calculations do not exist. The current set of rate constants for the reactions of H ̇atoms with both linear and branched C 5 alkenes, including their chemically activated pathways, are the first available in the literature of any reasonable fidelity for combustion modeling and are important for gasoline mechanisms. Validation of our theoretical results with pyrolysis experiments of 2-methyl-1-butene, 2-methyl-2-butene, and 3-methyl-1-butene at 2 bar in a single pulse shock tube (SPST) were carried out, with satisfactory agreement observed.

Hierarchical Study of the Reactions of Hydrogen Atoms with Alkenes: A Theoretical Study of the Reactions of Hydrogen Atoms with C2–C4 Alkenes

“…The current study uses the most recent ATcT values for the molecular and radical chaperones. 52 , 53 Similar to previous work, 4 , 5 ATcT, ANL0, and ANL1 formation enthalpies do not exist for the species Ċ 4 H 7 -11, Ċ 4 H 7 -12, Ċ 4 H 7 -13, Ċ 4 H 7 -14, Ċ 4 H 7 -22, iĊ 4 H 7 , and iĊ 4 H 7 -i1. Quantum chemical composite methods (CBS–QB3, CBS–APNO, G3, and G4) 55 − 57 were therefore used to calculate their formation enthalpies at 0 K via isodesmic reactions suitable for each species, using ATcT values as chaperones.…”

“…Jitariu et al 63 are in excellent agreement with our previous work for the reaction Ċ 5 H 11 -2 ↔ C 3 H 6 + Ċ 2 H 5 , 4 with the rate constants being within a factor of ∼1.3. The rate constant for the reaction aĊ 5 H 11 ↔ C 3 H 6 + Ċ 2 H 5 calculated in our most recent study 5 is a factor of ∼3 times faster at 500 K than our calculated rate constant for Ċ 5 H 11 -2 ↔ C 3 H 6 + Ċ 2 H 5 . 4 An energy barrier difference of 1.9 kJ mol –1 accounts for a factor of 1.6 of this difference.…”

“…The approximate variational calculation results from the current work for the alkene + Ḣ systems have been included in NUIGMech1.1, which includes our results from our previous studies of the pentene isomers. 4 , 5 The updated model, NUIGMech1.2, is used to simulate the recent results from a pyrolysis study of 1-alkenes using the NUIG single-pulse shock tube 32 and is represented by solid lines. Dashed lines represent model predictions of NUIGMech1.1.…”

“…Below are a list of some of the chemically activated pathways forming some of the major products of pyrolysis calculated in the current study and in previous ones. 4 , 5 C 3 H 6 + Ḣ ↔ [nĊ 3 H 7 ]* ↔ C 2 H 4 + ĊH 3 C 4 H 8 -1 + Ḣ ↔ [Ċ 4 H 9 -1]* ↔ C 2 H 4 + Ċ 2 H 5 C 4 H 8 -1 + Ḣ ↔ [Ċ 4 H 9 -2]* ↔ C 3 H 6 + ĊH 3 C 4 H 8 -2 + Ḣ ↔ [Ċ 4 H 9 -2]* ↔ C 3 H 6 + ĊH 3 iC 4 H 8 + Ḣ ↔ [iĊ 4 H 9 ]*↔ C 3 H 6 + ĊH 3 Moreover, chemically activated pathways were also found to be important for the reactions of Ḣ with the pentene isomers in our previous studies. 4 , 5 C 5 H 10 -1 + Ḣ ↔ [Ċ 5 H 11 -1]* ↔ C 2 H 4 + n-Ċ 3 H 7 C 5 H 10 -1 + Ḣ ↔ [Ċ 5 H 11 -2]* ↔ C 3 H 6 + Ċ 2 H 5 C 5 H 10 -2 + Ḣ ↔ [Ċ 5 H 11 -2]* ↔ C 3 H 6 + Ċ 2 H 5 C 5 H 10 -2 + Ḣ ↔ [Ċ 5 H 11 -3]* ↔ C 4 H 8 -1 + ĊH 3 aC 5 H 10 + Ḣ ↔ [aĊ 5 H 11 ]* ↔ C 3 H 6 + Ċ 2 H 5 aC 5 H 10 + Ḣ ↔ [aĊ 5 H 11 ]* ↔ C 4 H 8 -1 + ĊH 3 aC 5 H 10 + Ḣ ↔ [bĊ 5 H 11 ]* ↔ iC 4 H 8 + ĊH 3 bC 5 H 10 + Ḣ ↔ [bĊ 5 H 11 ]* ↔ iC 4 H 8 + ĊH 3 bC 5 H 10 + Ḣ ↔ [cĊ 5 H 11 ]* ↔ C 4 H 8 -2 + ĊH 3 cC 5 H 10 + Ḣ ↔ [cĊ 5 H 11 ]* ↔ C 4 H 8 -2 + ĊH 3 cC 5 H 10 + Ḣ ↔ [dĊ 5 H 11 ]* ↔ C 2 H 4 + iĊ 3 H 7...…”

“…In the current work, the reactions of Ḣ atoms with C 2 –C 4 alkenes are studied, while the reactions of Ḣ atom addition to C 5 alkenes were studied previously. 4 , 5 There have been a number of theoretical and experimental studies of Ḣ atoms with C 2 –C 4 alkenes. 17 − 16 This study aims to complement these by providing a comprehensive hierarchical set of rate constants for Ḣ atom addition and abstraction potential energy surfaces (PESs), including their chemically activated pathways for C 2 –C 5 alkenes, determined at the same levels of theory.…”