Theoretical calculations of structures, energetics, and kinetics of O (³P) + CH₃OH reactions

Abstract

DFT methods are used in calculations of geometries, energies, and frequencies for O ( 3 P) þ CH 3 OH reactions. CCSD(T) single-point calculations are carried out followed by extrapolation to the complete basis set (CBS) limit and inclusion of core correlation. The best estimate results of the reaction enthalpies (DH 0 0 ) for the first (À7.1 kcal/mol), second (2.0 kcal/mol), and the third (25.8 kcal/mol) reactions path are in excellent agreement with the experimental values, i.e., À7.2 6 0.2, 1.2 6 1.0, and 26.0 6 1.2 kcal/mol, respectively. Rate constants and activation energies in the range of 300-2,000 K calculated with the variational transition state theory are in good agreement with previous studies. H/D and 12 C/ 13 C kinetic isotope effects are also calculated in good agreement with available experimental data.

Computational Kinetics by Variational Transition-State Theory with Semiclassical Multidimensional Tunneling: Direct Dynamics Rate Constants for the Abstraction of H from CH3OH by Triplet Oxygen Atoms

“… a All computations except those from previous work ( c and d ) are based on geometries optimized by M08-HX/MG3S. b MUD­(6) is the mean unsigned deviation of the four classical barrier heights and two classical reaction energies from the best estimates, which are the results of the CCSDT(2) Q /CBS calculations. MUD(3) is the deviation of two classical barrier heights and the classical reaction energy of reaction R2 from the results of the CCSDT(2) Q /CBS calculations. c From Lu et al at B3LYP/6-311+G­(3df,2p) geometries. d From Alves et al . at BB1K/aug-cc-pVQZ geometries. …”

“… a Numbering of atoms is shown in Figure . b Used in Lu et al’s work. c Used in Alves et al’s work d Used in this work. e Values in parentheses are CCSD­(T) energies on B3LYP/6-311+G­(3df,2p) geometries. …”

“…15 (CCSD(T)), ref. 22 (BB1K), and present work including the first electronically excited state of the TS (M08-SO) and also without including it (M08-SO(ground-state)). For the BB1K method, Alves et al did not calculate the branching ratio, and therefore only total rate constants are plotted (cyan line) for their work.…”

“…It also should be noted that the values of the rate constants reported by Alves et al 22 have an error factor of 1.5 because they used a reaction symmetry number of 3 for reaction R1 instead of 2. As shown in Figure 2, the reactant and transition structure TS1 both have a symmetry C 1 , which means their rotational symmetry numbers are 1, but TS1 is chiral, and both structures lead to products, so in the harmonic-oscillator approximation that they used, the rate constant for reaction R1 has overall symmetry number of 2 107 (not 3).…”

Combination targeted therapy in advanced renal cell carcinoma

“…Our best estimate for the vibrationally adiabatic barrier height (Δ V a G,‡ ) indicates that R1 is the most important path in the overall reaction, followed by the addition of oxygen that occurs by breaking the CS bond (R3) and the substitution reaction (R4). For the isovalent reaction (CH 3 OH + O), the hydrogen abstraction from the methyl group has the lowest Δ V a G,‡ , followed by the hydrogen abstraction from the OH group and the breaking of the CO bond 57. Our best estimates of the Δ V a G,‡ values, given by the CCSD(T)/CBS//(BB1K or MP2)/aug‐cc‐pV(T+d)Z calculations for the R1–R4 paths are between 0.5 and 1.0 kcal mol −1 , 5.3 and 5.5 kcal mol −1 , 1.3 and 2.3 kcal mol −1 , and 1.6 and 2.9 kcal mol −1 , respectively.…”