Theoretical Study of Ni(N₄)₂, Ni(C₄H₄)₂, and Ni(C₂O₂)₂ Complexes

Ab initio molecular orbital theory and density functional theory have been applied to study the isoelectronic-liganded NiL2 (L = N42-, C4H42-, and C2O22-) sandwich complexes at the MP2/6-31G*, B3LYP/6-31G*, B3LYP/6-311+G*, and BHLYP/6-311+G(3df,3pd) levels of theory. The stable structure for Ni(N4)2 is a staggered conformer with D4d symmetry. The dissociation barriers for one N2 elimination and two N2 eliminations for Ni(N4)2 are 37.1 and 84.9 kcal/mol, respectively, at the B3LYP/6-31G* level of theory, which suggest that Ni(N4)2 is kinetically stable enough to resist dissociation. The calculated reaction energies for the dissociation of Ni(N4)2, Ni(C4H4)2, and Ni(C2O2)2 at the B3LYP/6-31G* level of theory suggest that both Ni(N4)2 and Ni(C2O2)2 are high-energy species; however, Ni(C4H4)2 is not

Direction Dynamics Study of the Hydrogen Abstraction Reaction CH₂O + NH₂ → CHO + NH₃

The hydrogen abstraction reaction CH2O + NH2 → CHO + NH3 has been studied using direct ab initio dynamics method. All of the information along the minimum energy path (MEP) was calculated at the UMP2/6-311+G(d, p) level of theory. Energetic data along the MEP were further refined using the scheme G2 with the UMP2/6-311+G(d, p) optimized geometries. The barrier heights for the forward and reverse reactions were obtained as 5.89 and 24.44 kcal/mol, respectively. Reaction rate constants and activation energies were calculated for the temperature range 250−2500 K by the improved canonical variation transition state theory (ICVT) incorporating a small-curvature tunneling correction (SCT). The rate constant at the room temperature was predicted to be 5.25 × 10-17 cm3 molecule-1 s-1, which is about 2 orders of magnitude smaller than that of the hydrogen abstraction reaction of acetaldehyde with aminogen

Mechanisms of Difluoroethylene Ozonolysis: A Density Functional Theory Study

We present a density functional theory (DFT) study on the mechanisms of gas-phase ozonolysis of three isomers of difluoroethylene, namely, cis-1,2-difluoroethylene, trans-1,2-difluoroethylene, and 1,1-difluoroethylene. MPW1K/cc-pVDZ and BHandHLYP/cc-pVDZ methods are employed to optimize the geometries of stationary points as well as the points on the minimum energy path (MEP). The energies of all the points were further refined at the QCISD(T)/cc-pVDZ and QCISD(T)/6-31+G(df,p) levels of theory with zero-point energy (ZPE) corrections. The ozone−cis-1,2-difluoroethylene reaction is predicted to be slower than the ozone−trans-1,2-difluoroethylene reaction. The enhanced reactivity of trans-1,2-difluoroethylene relative to the cis isomer is similar to the reactions of ozone with cis- and trans-dichloroethylene. The ozone−1,1-difluoroethylene reaction is predicted to be slower than the ozone−trans-1,2-difluoroethylene reaction. These results are in agreement with experimental studies. The calculated mechanisms indicate that in ozone−difluoroethylene reactions the yields of OH might be trivial, which is different from the reactions of ozone with unsaturated hydrocarbons

Ab Initio Study of the F + CH₃NHNH₂ Reaction Mechanism

The F + CH3NHNH2 reaction mechanism is studied based on ab initio quantum chemistry methods as follows: the minimum energy paths (MEPs) are computed at the UMP2/6-311++G(d,p) level; the geometries, harmonic vibrational frequencies, and energies of all stationary points are predicted at the same level of theory; further, the energies of stationary points and the points along the MEPs are refined by UCCSD(T)/6-311++g(3df,2p). The ab initio study shows that, when the F atom approaches CH3NHNH2, the heavy atoms, namely N and C atoms, are the favorable combining points. For the two N atoms, two prereaction complexes with Cs symmetry are generated and there exists seven possible subsequent reaction routes, of which routes 1, 2, 5, and 7 are the main channels. Routes 1, 2, and 5 are associated with HF elimination, with H from the amino group or imido group, and route 7 involves the N−N bond break. Routes 3 and 6 with relation to HF elimination with H from methyl, and route 4 involved the C−N bond break, are all energetically disfavored. For the C atom, the attack of F results in the break of the C−N bond and the products are CH3F + NHNH2. This route is very competitive