Yi-Zhen Tang

Theoretical and kinetic study of the H + C2H5CN reaction

The reaction of H radical with C2H5CN has been studied using various quantum chemistry methods. The geometries were optimized at the B3LYP/6‐311+G(d,p) and B3LYP/6‐311++G(2d,2p) levels. The single‐point energies were calculated using G3 and BMC‐CCSD methods based on B3LYP/6‐311++G(2d,2p) geometries. Four mechanisms were investigated, namely, hydrogen abstraction, C‐addition/elimination, N‐addition/elimination and substitution. The kinetics of this reaction were studied using the transition state theory and multichannel Rice‐Ramsperger‐Kassel‐Marcus methodologies over a wide temperature range of 200–3000 K. The calculated results indicate that C‐addition/elimination channel is the most feasible over the whole temperature range. The deactivation of initial adduct C2H5CHN is dominant at lower temperature with bath gas H2 of 760 Torr; whereas C2H5+HCN is the dominant product at higher temperature. Our calculated rate constants are in good agreement with the available experimental data.

Theoretical study and rate constant calculation for the O(3P) + C2H5CN reaction

The complicated microscopic reaction mechanisms of O(3P) with C2H5CN on the ground electronic state energy surface have been investigated at the G3(MP2) level of theory based on the geometric parameters optimized at the B3LYP/6-311 + G(d, p) level. Two kinds of H-abstraction and addition–elimination channels are considered, namely methylene-H abstraction, methyl-H abstraction, C-addition/elimination and N-addition/elimination. The kinetics of the title reaction have been studied using the TST and multichannel RRKM methodologies over a wide temperature range of 200–2000 K. The results show that the methylene-H abstraction process is predominant for the whole reaction. With an increase of temperature, H-abstraction from the methyl position channel should be taken into account. The C-addition/elimination process provides a few contributions to the title reaction compared with two kinds of H-abstraction channels over the whole temperature region and the N-addition/elimination channel can be negligible due to the high entrance barrier and unstable products.

Theoretical study of the hydrogen abstraction reaction of CH3OH with NCO

A direct dynamics method is employed to study the mechanism and kinetics of the hydrogen abstraction reaction of CH3OH with NCO. The optimized geometries and frequencies of the stationary points and the minimum-energy paths (MEPs) are obtained at the MP2/6-311G(d,p) level. In order to obtain more accurate potential energy surface (PES) information and provide more credible energy data for kinetic calculation, the single-point energies along the MEPs are further computed at QCISD(T)/6-311+G(d,p) and G3MP2 levels. The rate constants for two channels, the methyl-H abstraction channel and hydroxyl-H abstraction channel, are calculated by canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over the wide temperature region 220–1500 K. The theoretical overall rate constants are in good agreement with the available experimental data. For the title reaction, the methyl-H abstraction channel is dominant, while the hydroxyl-H abstraction channel is negligible over the whole temperature region.

Mechanistic and kinetic investigations of N2H4 + OH reaction.

The reaction of N2H4 with OH has been investigated by quantum chemical methods. The results show that hydrogen abstraction mechanism is more feasible than substitution mechanism thermodynamically. The calculated rate constants agree with the available experimental data. The calculated results show that the variational effect is small at lower temperature region, while it becomes significant at higher temperature region. On the other hand, the small‐curvature tunneling effect may play an important role in the temperature range 220−3000 K. Moreover, the calculated rate constants show negative temperature dependence at the temperatures below 500 K, which is in accordance with Vaghjianis report that slightly negative temperature dependence is found over the temperature range of 258−637 K. The mechanism of the major product (N2H3) with OH has also been investigated theoretically to understand the title reaction thoroughly.

Theoretical study of mechanisms for NCO with CH3 reaction

A detailed computational study has been performed at the QCISD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) level for the NCO with CH3 reaction by constructing singlet and triplet potential energy surfaces (PES). The results show that the title reaction is more favorable for the singlet PES than the triplet PES. On the singlet PES, the dominant channel is the barrierless addition of the O or N atom to the C atom of the methyl group to form CH3NCO (IM1) and CH3OCN (IM2). On the triplet PES, the favorable channel is the barrierless addition of the N atom to the C atom of the methyl group to form an intermediate CH3NCO (3IM2), which then undergoes a N–C bond scission process to give out CH3N + CO.

Theoretical study on the mechanism for the reaction of pentafulvenone with HNC in singlet and triplet states, interconversions and solvation effect

The mechanism for the reaction of pentafulvenone with HNC in singlet and triplet states is studied theoretically at MP2/6-311+G**//B3LYP/6-311+G** level. Eleven singlet and two triplet stable points, 21 singlet and 11 triplet transition states are found. The results show that the reaction has two attacking modes, which are HNC attacking carbon–oxygen and carbon–carbon double bond of pentafulvenone. The reaction is more favourable in singlet state, and the dominant pathway is to form cyclopentadienyl isocyanide P via TS6. The structure of the most stable product is identified. The interconversions between cyclopentadienyl isocyanides and cyclopentadienyl cyanides are thoroughly studied in the singlet state. In aqueous solvent, the reaction of pentafulvenone with HNC are investigated using the PCM-UAHF model at the MP2 (PCM)/6-311+G**//B3LYP (PCM)/6-311+G** and MP2 (PCM)/6-311+G**//B3LYP/6-311+G** levels. The barrier of the transition state in the main pathway is decreased.

Direct ab initio dynamics calculations of the reaction rate for the hydrogen abstraction reaction of NCO with CH4 and C2H6

The kinetics of the hydrogen abstraction reactions NCO + CH4 (R1) and NCO + C2H6 (R2) have been studied over a wide temperature range. The minimum energy paths (MEPs) were calculated at the MP2/cc-pVDZ level and single-point calculations were refined at the G3MP2 level. The rate constants for the title reactions were calculated using canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions. The fitted three-parameter formulae are k 1 = 2.52 × 10−22 T 3.46 exp(2466/T) and k 2 = 9.8 × 10−22 T 3.2 exp(411.8/T) cm3 molecule−1 s−1 for (R1) and (R2), respectively. The calculated rate constants were found to be in good agreement with the available experimental data. Deuterium kinetic isotope effects were also investigated. Both reactions show a significant kinetic isotope effect in the low-temperature range.