Benchmark ab initio stationary-point characterization of the complex potential energy surface of the multi-channel Cl + CH₃NH₂ reaction

Abstract

We characterize the exothermic low/submerged-barrier hydrogen-abstraction (HCl + CH2NH2/CH3NH) as well as, for the first time, the endothermic high-barrier amino-substitution (CH3Cl + NH2), methyl-substitution (NH2Cl + CH3), and hydrogen-substitution (CH2ClNH2/CH3NHCl...

Benchmark Ab Initio Characterization of the Abstraction and Substitution Pathways of the Cl + CH3CN Reaction

“…However, recent studies 23 , 24 , 32 revealed that several other product channels are also possible such as H + CH 2 ClNH 2 , H + CH 3 NHCl, NH 2 + CH 3 Cl, and CH 3 + NH 2 Cl in the case of the Cl + CH 3 NH 2 reaction. 32 Quantum chemical computations can determine the reaction enthalpies and barrier heights for these processes, thereby revealing their thermodynamic and kinetic requirements, respectively. Even if some of these pathways may proceed over high barriers and cannot occur at standard thermal conditions, they may be accessible by crossed-beam techniques at hyperthermal collision energies as Minton and co-workers 33 did in the case of the O( 3 P) + CH 4 /C 2 H 6 /C 3 H 8 reactions revealing novel reaction pathways such as H substitution, CH 3 substitution, etc.…”

Benchmark ab initio potential energy surface mapping of the F + CH3NH2 reaction

“…As we published in our previous work, 22 in the reaction of Cl + CH 3 NH 2 there are six reaction channels, as in the title reaction: two hydrogen-abstraction pathways from the two functional groups and are four substitution pathways, where the halogen atom substitutes the amino/methyl group or one hydrogen of these. When methylamine reacts with the fluorine atom, the reaction channels are more exothermic than in the case of reaction with chlorine; however, in both cases the CH 3 HA products have the lowest relative energy and the NH 2 HS products have the highest.…”

“…During the characterization of the potential energy surface, we build upon previous work 7,22 and chemical intuition to identify the important stationary points of the F + CH 3 NH 2 reaction. We use the restricted open-shell second-order Møller–Plesset perturbation theory (RMP2) 24 and the correlation-consistent aug-cc-pVDZ basis set 25 to determine the primary geometries, energies and harmonic vibrational frequencies.…”

“…What comes after the previous work on the title reaction? First, it is important to note that the previous computations only considered the H-abstraction channels, whereas our recent studies on the F/Cl/Br/I/OH + C2H6 20,21 and Cl + CH3NH2/CH3CN 22,23 reactions revealed several other channels such as hydrogen and methyl substitution for the reactions of C2H6 and the picture is even more complex in the cases of CH3NH2 and CH3CN. Thus, in the present study, we plan to characterize all the possible, chemically relevant pathways of the title reaction, thereby providing new qualitative insights into the mechanisms of the F + CH3NH2 process.…”

“…These two channels are exothermic in the title reaction, but in the case of Cl + CH3NH2 these are endothermic.The two additional kinetically hindered product channels are investigated in the title reaction as well, where two bonds are required to break and form leading to NH3 + CH2F and CH4 + NHF. The products of the former channel have ∆E(∆H0) = −29.65(−32.77) kcal mol−1 relative energy and of the latter have ∆E(∆H0) = 3.87 (0.03) kcal mol −1 , whereas the corresponding values for the Cl + CH3NH2 system are −3.70(−8.20) and 14.24(9.82) kcal mol −1 , respectively 22. In both reactions, the exothermic NH3 formation is thermodynamically competitive with H-abstractions, however, the former may have much higher barrier due to the two bond cleavages required to form the NH3 + CH2F/CH2Cl products.…”