An ab initio/Rice–Ramsperger–Kassel–Marcus prediction of rate constant and product branching ratios for unimolecular decomposition of propen-2-ol and related H+CH2COHCH2 reaction

Abstract

Enols have been found to be important intermediates in the combustion flames of hydrocarbon [C. A. Taatjes et al., Science 308, 1887 (2005)]. The removal mechanism of enols in combustion flame has not been established yet. In this work, the potential energy surface for the unimolecular decomposition of syn-propen-2-ol and H + CH(2)COHCH(2) recombination reactions have been first investigated by CCSD(T) method. The barrier heights, reaction energies, and geometrical parameters of the reactants, products, intermediates, and transition states have been investigated theoretically. The results show that the formation of CH(3)CO + CH(3) via the CH(3)COCH(3) intermediate is dominant for the unimolecular decomposition of syn-propen-2-ol and its branching ratio is over 99% in the whole temperature range from 700 to 3000 K, and its rate constant can be expressed as an analytical form in the range of T=700-3000 K at atmospheric pressure. This can be attributed to the lower energy barrier of this channel compared to the other channels. The association reaction of H with CH(2)COHCH(2) is shown to be a little more complicated than the unimolecular decomposition of syn-propen-2-ol. The channel leading to CH(3)CO + CH(3) takes a key role in the whole temperature range at atmospheric pressure. However at the higher pressure of 100 atm, the recombination by direct formation of syn-propen-2-ol through H addition is important at T<1000 K. In the range of T>1400 K, the recombination channel leading to CH(3)CO + CH(3) turns out to be significant.

Substitution Reactions in the Pyrolysis of Acetone Revealed through a Modeling, Experiment, Theory Paradigm

“…Prior theoretical studies , of 2-propenol decomposition are consistent with this assessment. However, back-isomerization of the enol (−) forms chemically activated acetone (CH 3 C­(O)­CH 3 *), which can then rapidly dissociate via This competition between stabilization to acetone (−) and subsequent dissociation of chemically activated acetone to radical products via () was not characterized in the prior theoretical studies. , Master equation calculations were performed with the VRC-TST results for the CC fission channel from Saxena et al . for () coupled with TST predictions for () using the energies (and molecular parameters) from the present CCSD­(T)/CBS//M06-2X/cc-pVTZ calculations.…”

“…Prior theoretical studies 81,82 of 2-propenol decomposition are consistent with this assessment. However, back-isomerization of the enol (−R6) forms chemically activated acetone (CH 3 C(O)CH 3 *), which can then rapidly dissociate via…”

“…Computational energies include zero-point corrections. b Δ r H ° (0 K) for the listed decomposition reactions of acetone from Active Thermochemical Tables, using the Thermochemical Network ver. 1.122v. c CCSD­(T)/CBS­(cc-pVTZ,cc-pVQZ)//M06-2X/cc-pVTZ. d CCSD­(T)/6-311+G­(3df,2p)//B3LYP/6-311G­(d,p) from ref . e CCSD­(T)/aug-cc-pVDZ+2df//MP2/6-311++G­(2d,2p) from ref . f The primary entries are CASPT2 based entries, while the numbers in italics denote Davidson corrected MRCI based results. Both are tied back to the acetone energy through the ANL0 value for CH 3 + CH 3 CO as described in the text.…”

“…This competition between stabilization to acetone (−R6) and subsequent dissociation of chemically activated acetone to radical products via (R7) was not characterized in the prior theoretical studies. 81,82 Master equation calculations were performed with the VRC-TST results for the CC fission channel from Saxena et al 83 for (R1) coupled with TST predictions for (R6) using the energies (and molecular parameters) from the present CCSD(T)/CBS//M06-2X/cc-pVTZ calculations. 3.2.…”

Calculation of Arrhenius Parameters by the Rrkm Method for the Carbon–Hydrogen Bond Fission Reaction of Fluorobenzene

“…In this paper, we discuss our implementation of Rice-Ramsperger-Kassel-Marcus (RRKM) theory to predict the microcanonical and canonical rate constants for C-H bond fission of FB. Calculation of microcanonical rate constants has been an important subject area in chemical kinetics investigations for many years because it can be applied not just to make a www.prkm.co.uk full prediction of rate, but also to obtain rate constants with certain conserved quantum numbers such as the total angular momentum [5][6][7][8][9][10]. RRKM theory is a well-established method that assumes rapid energy distribution in vibrational and rotational motions of molecules and the existence of a transition state between reactant and product.…”