Implementation of a variational code for the calculation of rate constants and application to barrierless dissociation and radical recombination reactions: CH₃OH = CH₃ + OH

Abstract

Here, a new implementation for calculating canonical variational rate constants is introduced and tested against methanol dissociation rate constants and the (high pressure) radical recombination reaction, CH 3 þ OH ! CH 3 OH. Reaction paths are described at the CASSCF level, with energy corrections at MRMP2. Molecular properties for both stationary and non-stationary points along the reaction path are used for the calculation of rate constants. Different models for the low vibrational frequencies are discussed: harmonic oscillator and free rotor models. The CH 3 þ OH ! CH 3 OH recombination rate constants are determined from dissociation rate constants and equilibrium constants. Our calculated rate constants agree with previously reported data for these reactions, suggesting the good performance of our implemented code in calculating canonical variational rate constants. The rate expressions are suggested: as: k dis (T) ¼ 8.42 Â 10 þ16 Â e À96.18/RT and k rec (T) ¼ 2.05 Â 10 À10 Â (T/298) À0.24 Â e À0.30/RT , in units s À1 and cm 3 molecule À1 s À1 , respectively, and over the temperature range 300-2000 K, with activation energies in kcal/mol.

Quantitative Structure–Property Relationship (QSPR) Models for a Local Quantum Descriptor: Investigation of the 4- and 3-Substituted-Cinnamic Acid Esterification

“…A series of 10 ethyl 4- or 3-X-cinnamates were synthesized from 4- or 3-X-cinnamic acid with ethanol, in accordance with the literature [10], where X = 4-OCH 3 , 4-OH, 4-CH 3 electron donor groups (EDGs), 3-F, 3-NO 2 , 4-Cl, 4-F, 4-CN, 4-NO 2 electron withdrawing (EWGs) groups and X = H. The reactions were conducted under reflux for 30 h using sulfuric acid as catalyst, to furnish the ethyl 4- or 3-X-cinnamates in good yields (45%–80%), and that the compounds with EWGs presented the best results. The compounds were obtained in trans geometry, being confirmed by the values of the coupling constant ( J ) of the olefinic hydrogens in the range of 15.0–16.5 Hz [47].…”

“…These can be expressed as charges, highest occupied molecular orbital (HOMO) and unoccupied molecular orbital (LUMO) energies, (HOMO-LUMO gap), Fukui function, and FERMOS (Frontier Effective-for-Reaction Molecular Orbitals) quantum descriptors [7]. Due to the importance of the cinnamates, and considering the interest both in studying the electronic effects arising from different substituents in cinnamoyl moiety [8,9] and in investigating the fundamental aspects that can elucidate the dynamic of chemical reactions [10,11], we report here theoretical-experimental results with the aim of describing a selection of quantum descriptors for the local hardness of carbonyl in the 4- and 3-substituted-cinnamic acid esterification being the substituents effects measured by quantitative structure–property relationship (QSPR). In order to assess such quantum descriptors, theoretical calculations have been performed at the density functional theory (DFT) level for a series of ethyl 4- and 3-substituted-cinnamates.…”

Rate Constants and Sticking Coefficients for H2 and He Obtained by Analysis of Agglomeration in a Nozzle Beam

“…It is of course possible to calculate rate constants using molecular dynamics or other methods . However, calculations are normally limited to reactions involving a small number of nuclei.…”

“…However, calculations are normally limited to reactions involving a small number of nuclei. Published results are for particular reactions of interest, never for a whole class of reactions involving many nuclei. It is unlikely that values for many rate constants could be obtained in this way.…”

Unrestricted Floating Orbitals for the Investigation of Open Shell Systems

“…Another investigation considers the methyl radical to assess the accuracy of the spin-projected unrestricted Hartree-Fock method by investigating electron and spin densities (Glaser & Choy, 1993). Furthermore, reactions with other small molecules like carbon monoxide (Das & Lee, 2014), the recombination reaction with OH radicals (Oliveira & Bauerfeldt, 2012), and even the role in methanol synthesis (Zakharov, Ijagbuji, Tselishtev, Loriya, & Fedotov, 2015) have been studied recently. Due to its high reactivity, the methyl radical is involved in reactions which comprise the abstraction of a hydrogen atom so that many recent studies deal with the kinetic properties of these reactions (Mendes, Zhou, & Curran, 2014), (Saheb, 2015), (Tan, Yang, Krauter, Ju, & Carter, 2015).…”