Quantum chemical investigation of formation of polychlorodibenzo-p-dioxins and dibenzofurans from oxidation and pyrolysis of 2-chlorophenol

Density functional theory (DFT) calculations have been used to obtain thermochemical parameters for formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/PCDF) from the oxidation of 2-chlorophenol. Formation mechanisms of PCDD through radical-radical coupling have been investigated in detail. The sequence of 2-chlorophenoxy radical coupling has been studied. The formation of chlorinated bis keto dimers which results from cross coupling of 2-chlorophenoxy at the ortho carbon bearing hydrogen (a known direct route for PCDF formation) passes through a tight transition structure whose barrier is 9.4 kcal/mol (0 K). Three routes for the formation of the most abundant PCDD/PCDF species (viz., 4,6-dichlorodibenzofuran, 4,6-DCDF, and 1-monochlorodibenzo-p-dioxin, 1-MCDD) in oxidation and pyrolysis of 2-chlorophenol are discussed. In the case of 4,6-DCDF, formation through H or HO + keto-keto <==> H2 or H2O + keto-keto* <==> H2 or H2O + enol-keto* <==> H2 or H2O + 4,6-DCDF + HO is shown to be the preferred route. The other two routes proceed via closed shell processes (keto-keto <==> enol-keto <==> enol-enol <==> H2O + 4,6-DCDF) and (keto-keto <==> enol-keto <==> (H-,OH-) 4,6-DCDF <==> H2O + 4,6-DCDF). Results indicate that 1-MCDD should be the favored product in 2-chlorophenol pyrolysis in agreement with experimental findings. According to our results, tautomerization (inter-ring hydrogen transfer) and intra-annular displacement of HCl would not be competitive with paths deriving from H abstraction from the phenolic oxygen and the benzene ring followed by displacement of Cl in the formation of dibenzo-p-dioxin (DD) and 1-MCDD. The results presented here will assist in construction of detailed kinetic models to account for the formation of PCDD/PCDF from chlorophenols.     

Thermal decomposition of methyl butanoate: ab initio study of a biodiesel fuel surrogate

In this paper, we report a detailed analysis of the breakdown kinetic mechanism for methyl butanoate (MB) using theoretical approaches. Electronic structures and structure-related molecular properties of reactants, intermediates, products, and transition states were explored at the BH&HLYP/cc-pVTZ level of theory. Rate constants for the unimolecular and bimolecular reactions in the temperature range of 300-2500 K were calculated using Rice-Ramsperger-Kassel-Marcus and transition state theories, respectively. Thirteen pathways were identified leading to the formation of small compounds such as CH(3), C(2)H(3), CO, CO(2), and H(2)CO. For the initial formation of MB radicals, H, CH(3), and OH were considered as reactive radicals participating in hydrogen abstraction reactions. Kinetic simulation results for a high temperature pyrolysis environment show that MB radicals are mainly produced through hydrogen abstraction reactions by H atoms. In addition, the C(O)OCH(3) = CO + CH(3)O reaction is found to be the main source of CO formation. The newly computed kinetic sub-model for MB breakdown is recommended as a core component to study the combustion of oxygenated species.     

Mechanistic and kinetic study of the O + CH2OH reaction

The mechanism for the O + CH2OH reaction was investigated by various ab initio quantum chemistry methods. For the chemical activation mechanism, that is, the addition/elimination path, the couple-cluster methods including CCSD and CCSD(T) were employed with the cc-pVXZ (X = D, T, Q, 5) basis sets. For the abstraction channels, multireference methods including CASSCF, CASPT2, and MRCISD were used with the cc-pVDZ and cc-pVTZ basis sets. It has been shown that the production of H + HCOOH is the major channel in the chemical activation mechanism. The minor channels include HCO + H2O and OH + CH2O. The hydrogen abstraction by an O atom from the CH2OH radical produces either OH + CH2O or OH + HCOH. Moreover, the two abstraction reactions are essentially barrierless processes. The rate constants for the association of O with CH2OH have been calculated using the flexible transition state theory. A weak negative temperature dependence of the rate constants is found in the range 250-1000 K. Furthermore, it is estimated that the abstraction processes also play an important role in the O + CH2OH reaction. Additionally, the falloff behavior for the OCH2OH --> H + HCOOH reaction has been investigated. The present theoretical results are compared to the experimental measurements to understand the mechanism and kinetic behavior of the O + CH2OH reaction and the unimolecular reaction of the OCH2OH radical.     

Remarkable Differences in Amine Substitution Reactions of Trichloromethyl and Trifluoromethyl Difluorophosphines,CX3PF2 (X = F,Cl): A Computational Study

Detailed computational studies have been carried out to explain the unexpected differing reactions that occur between dimethylamine and the difluorophosphines, CX₃PF₂ (X = F, Cl). The reaction affords the thermodynamically controlled product chloroform in the case of X = Cl, whereas when X = F the analogous reaction pathway leading to fluoroform is hindered by a substantial reaction barrier in the gas phase, where the reaction should take place due to the volatility of the reactant. While the gas‐phase reaction energy gap is somewhat reduced when X = Cl, due to the stability of the migrating CCl₃⁻ moiety, the still substantial barrier does not account for the chloroform formation. Polarizable continuum model (PCM) calculations indicate a reduction of the barrier, facilitating the liquid‐phase reaction. The alternative gas‐phase reaction path, resulting in the aminolysis of a P—F bond is reversible and is shifted toward the product by capturing HF as the dimethylamino salt of the [CF₃PF₄H]⁻ anion.     

C2H3＋NO2反应速率常数的研究

利用激光光解C2H3Br产生C2H3自由基,在气相298 K, 总压2.66×103 Pa的条件下,研究C2H3与NO2的反应,用激光光解-激光诱导荧光（LP-LIF）检测中间产物OH自由基的相对浓度随着反应时间的变化关系,报导了双分子反应C2H3＋NO2的速率常数k(C2H3＋NO2)=(1.8±0.05)×10－11cm3•molec.－1•s－1,同时也得到OH＋NO2反应的速率常数k(OH＋NO2)=(2.1±0.15)×10－12 cm3•molec.－1•s－1.     

HCHO+X(X=F、Cl、Br)的反应机理

采用CCSD/6-311++G(d,p)//B3LYP/6-311++G(d,p)方法研究了HCHO与卤素原子X(X=F、Cl、Br)的反应机理. 计算结果表明, 卤素原子X(X=F、Cl、Br)主要通过直接提取HCHO中的H原子生成HCO+HX(X=F、Cl、Br). 另外还可以生成稳定的中间体, 中间体再通过卤原子夺氢和氢原子直接解离两个反应通道分别生成HCO+HX(X=F、Cl、Br)和H+XCHO(X=F、Cl、Br). 其中卤原子夺氢通道为主反应通道, HCO和HX(X=F、Cl、Br)为主要的反应产物; 且三个反应的活化能均较低, 说明此类反应很容易进行, 计算结果与实验结果符合很好. 电子密度拓扑分析显示, 在HCHO+X反应通道(b)中出现了T型结构过渡态, 结构过渡态(STS)位于能量过渡态(ETS)之后. 并且按F、Cl、Br的顺序, 结构过渡态出现得越来越晚.     

A study of the unimolecular dissociation of the 2-buten-2-yl radical via the 193 nm photodissociation of 2-chloro-2-butene

This work investigates the unimolecular dissociation of the 2-buten-2-yl radical. This radical has three potentially competing reaction pathways: C-C fission to form CH3 + propyne, C-H fission to form H + 1,2-butadiene, and C-H fission to produce H + 2-butyne. The experiments were designed to probe the branching to the three unimolecular dissociation pathways of the radical and to test theoretical predictions of the relevant dissociation barriers. Our crossed laser-molecular beam studies show that 193 nm photolysis of 2-chloro-2-butene produces 2-buten-2-yl in the initial photolytic step. A minor C-Cl bond fission channel forms electronically excited 2-buten-2-yl radicals and the dominant C-Cl bond fission channel produces ground-state 2-buten-2-yl radicals with a range of internal energies that spans the barriers to dissociation of the radical. Detection of the stable 2-buten-2-yl radicals allows a determination of the translational, and therefore internal, energy that marks the onset of dissociation of the radical. The experimental determination of the lowest-energy dissociation barrier gave 31 +/- 2 kcal/mol, in agreement with the 32.8 +/- 2 kcal/mol barrier to C-C fission at the G3//B3LYP level of theory. Our experiments detected products of all three dissociation channels of unstable 2-buten-2-yl as well as a competing HCl elimination channel in the photolysis of 2-chloro-2-butene. The results allow us to benchmark electronic structure calculations on the unimolecular dissociation reactions of the 2-buten-2-yl radical as well as the CH3 + propyne and H + 1,2-butadiene bimolecular reactions. They also allow us to critique prior experimental work on the H + 1,2-butadiene reaction.     

Ionization of ozone/chlorofluorocarbon mixtures in atmospheric gases: formation and remarkable dissociation of

The reactions occurring upon ionization of mixtures containing ozone and CHX2Y (X = H, Cl, F; Y = Cl, F) halocarbons diluted in atmospheric gases (O2, N2) have been investigated in detail by mass spectrometric and theoretical methods. In all systems investigated the reactivity pattern is characterized by the preliminary formation of [CHXY x O3+] adducts which undergo unimolecular dissociation into HXYO2+ and CO. This remarkable dissociation which requires extensive molecular reorganization is exceptional for hydrogenated halocarbons. The work represents the first systematic study of the ionic chemistry in systems containing both ozone and halocarbons diluted in atmospheric gases.     

13C, 18O, and D fractionation effects in the reactions of CH3OH isotopologues with Cl and OH radicals

A relative rate experiment is carried out for six isotopologues of methanol and their reactions with OH and Cl radicals. The reaction rates of CH2DOH, CHD2OH, CD3OH, (13)CH3OH, and CH3(18)OH with Cl and OH radicals are measured by long-path FTIR spectroscopy relative to CH3OH at 298 +/- 2 K and 1013 +/- 10 mbar. The OH source in the reaction chamber is photolysis of ozone to produce O((1)D) in the presence of a large excess of molecular hydrogen: O((1)D) + H2 --> OH + H. Cl is produced by the photolysis of Cl2. The FTIR spectra are fitted using a nonlinear least-squares spectral fitting method with measured high-resolution infrared spectra as references. The relative reaction rates defined as alpha = k(light)/k(heavy) are determined to be: k(OH + CH3OH)/k(OH + (13)CH3OH) = 1.031 +/- 0.020, k(OH + CH3OH)/k(OH + CH3(18)OH) = 1.017 +/- 0.012, k(OH + CH3OH)/k(OH + CH2DOH) = 1.119 +/- 0.045, k(OH + CH3OH)/k(OH + CHD2OH) = 1.326 +/- 0.021 and k(OH + CH3OH)/k(OH + CD3OH) = 2.566 +/- 0.042, k(Cl + CH3OH)/k(Cl + (13)CH3OH) = 1.055 +/- 0.016, k(Cl + CH3OH)/k(Cl + CH3(18)OH) = 1.025 +/- 0.022, k(Cl + CH3OH)/k(Cl + CH2DOH) = 1.162 +/- 0.022 and k(Cl + CH3OH)/k(Cl + CHD2OH) = 1.536 +/- 0.060, and k(Cl + CH3OH)/k(Cl + CD3OH) = 3.011 +/- 0.059. The errors represent 2sigma from the statistical analyses and do not include possible systematic errors. Ground-state potential energy hypersurfaces of the reactions were investigated in quantum chemistry calculations at the CCSD(T) level of theory with an extrapolated basis set. The (2)H, (13)C, and (18)O kinetic isotope effects of the OH and Cl reactions with CH3OH were further investigated using canonical variational transition state theory with small curvature tunneling and compared to experimental measurements as well as to those observed in CH4 and several other substituted methane species.     

Theoretical study of the reactions CF3CH2OCHF2 + OH/Cl and its product radicals and parent ether(CH3CH2OCH3) with OH

A dual-level direct dynamic method is employed to study the reaction mechanisms of CF3CH2OCHF2 (HFE-245fa2; HFE-245mf) with the OH radicals and Cl atoms. Two hydrogen abstraction channels and two displacement processes are found for each reaction. For further study, the reaction mechanisms of its products (CF3CH2OCF2 and CF3CHOCHF2) and parent ether CH3CH2OCH3 with OH radical are investigated theoretically. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the B3LYP/6-311G(d,p) level. The energetic information along the MEPs is further refined at the G3(MP2) level of theory. For reactions CF3CH2OCHF2 + OH/Cl, the calculation indicates that the hydrogen abstraction from --CH2-- group is the dominant reaction channel, and the displacement processes may be negligible because of the high barriers. The standard enthalpies of formation for the reactant CF3CH2OCHF2, and two products CF3CH2OCHF2 and CF3CHOCHF2 are evaluated via group-balanced isodesmic reactions. The rate constants of reactions CF3CH2OCHF2 + OH/Cl and CH3CH2OCH3 + OH are estimated by using the variational transition state theory over a wide range of temperature (200-2000 K). The agreement between the theoretical and experimental rate constants is good in the measured temperature range. From the comparison between the rate constants of the reactions CF3CH2OCHF2 and CH3CH2OCH3 with OH, it is shown that the fluorine substitution decreases the reactivity of the C--H bond.     

Kinetic Relationships between Reactions in the Gas Phase and in Solution

Some recent examples of reactions proceeding both in the gas phase and in solution have been investigated to determine their kinetics and mechanisms. The ratio of the corresponding rate constants, k_G and k_L, of the elementary processes studied has been found to be about unity for unimolecular reactions and between 1 and 10 for bimolecular reactions. The mechanisms, overall rates, rate constants, and activation energies have been determined for the homogeneous gas reaction NOCl + Cl₂O = NO₂Cl + Cl₂ and the reaction NOCl + N₂O₅ = NO₂Cl + 2 NO₂, carried out in C₂F₃Cl₃.     

Experimental and theoretical study of the carbon-13 and deuterium kinetic isotope effects in the Cl and OH reactions of CH3F

A laser flash photolysis-resonance fluorescence technique has been employed to determine absolute rate coefficients for the CH3F + Cl reaction in N2 bath gas in the temperature range of 200-700 K and pressure range of 33-133 hPa. The data were fitted to a modified Arrhenius expression k(T) = 1.14 x 10(-12) x (T/298)2.26 exp{-313/T}. The OH and Cl reaction rates of (13)CH3F and CD3F have been measured by long-path FTIR spectroscopy relative to CH3F at 298 +/- 2 K and 1013 +/- 10 hPa in purified air. The FTIR spectra were fitted using a nonlinear least-squares spectral fitting method including line data from the HITRAN database and measured infrared spectra as references. The relative reaction rates defined by alpha = k(light)/k(heavy) were determined to be k(OH+CH3F)/k(OH+CD3F) = 4.067 +/- 0.018, k(OH+CH3F)/k(OH+(13)CH3F) = 1.067 +/- 0.006, k(Cl+CH3F)/k(Cl+CD3F) = 5.11 +/- 0.07, and k(Cl+CH3F)/k(Cl+(13)CH3F) = 1.016 +/- 0.006. The carbon-13 and deuterium kinetic isotope effects in the OH and Cl reactions of CH3F have been further investigated by quantum chemistry methods and variational transition state theory.     

Cover Picture: Journal of the Chinese Chemical Society 5/2012

Oriented molecular beams provide us direct microscopic information on reaction dynamics in bimolecular as well as photodissociation systems. The oriented & crossed beam experiment of OH + HBr → H₂O + Br reveals the steric effect which clarifies branching mechanisms. Collisions at O‐end of OH lead to direct H₂O formation while H‐end of OH reacts via indirect migration mechanism. A roaming pathway is observed along with transition‐state pathway in photodissociation of methyl formate HCOOCH₃ which can be a unimolecular version of branching dynamics at the molecular level. For more details on this figure, please see pp 567～582 in this issue.     

State-specific reactions of Cu(+)(1S, 3D) with CH3X and CF3X (X = Cl, Br, I): exploring the influence of dipole orientation on association and C-X bond activation

The reactions of gas-phase Cu(+)((1)S) and Cu(+)((3)D) with CF(3)X and CH(3)X (X = Cl, Br, and I) have been examined experimentally using the drift cell technique at 3.5 Torr in He at room temperature. State-specific product channels and overall bimolecular rate constants for depletion of the two Cu(+) states were determined using electronic state chromatography. The results showed that Cu(+)((1)S) participates exclusively in association with all of these neutrals, whereas, depending on the neutral, Cu(+)((3)D) initiates up to three bimolecular processes, resulting in the formation of CuX(+), CuC(H/F)(3)(+), and C(H/F)(3)X(+). Possible structures for the singlet association products were explored using density functional methods. These calculations indicated that Cu(+) preferentially associates with the labile halogen (Cl, Br, I) with all neutrals except CF(3)Cl, for which a "backside" geometry occurs in which Cu(+)((1)S) is weakly bound to the -CF(3) end of the molecule. All products observed on the triplet reaction surface can be understood in terms of either known or calculated thermochemical requirements. Product distributions and overall reaction efficiencies for C-X bond activation (X = Br, I) through Cu(+)((3)D) suggest that the orientation of the neutral dipole has little or no effect in controlling access to specific product channels. Likewise, second-order rate constants for reactions with X = Br and I indicate efficient depletion of Cu(+)((3)D) and do not exhibit the dramatic variations in reaction efficiency previously observed with CH(3)Cl and CF(3)Cl. These results suggest that C-X bond activation proceeds through a bond-insertion mechanism as opposed to direct abstraction.     

Comprehensive theoretical studies on the gas phase SN2 reactions of anionic nucleophiles toward chloroamine and N-chlorodimethylamine with inversion and retention mechanisms

The anionic S(N)2 reactions at neutral nitrogen, Nu(-) + NR(2)Cl → NR(2)Nu + Cl(-) (R = H, Me; Nu = F, Cl, Br, OH, SH, SeH, NH(2), PH(2), AsH(2)) have been systematically studied computationally at the modified G2(+) level. Two reaction mechanisms, inversion and retention of configuration, have been investigated. The main purposes of this work are to explore the reactivity trend of anions toward NR(2)Cl (R = H, Me), the steric effect on the potential energy surfaces, and the leaving ability of the anion in S(N)2@N reactions. Our calculations indicate that the complexation energies are determined by the gas basicity (GB) of the nucleophile and the electronegativity (EN) of the attacking atom, and the overall reaction barrier in the inversion pathway is basically controlled by the GB value of the nucleophile. The retention pathway in the reactions of NR(2)Cl with Nu(-) (Nu = F, Cl, Br, OH, SH, SeH) is energetically unfavorable due to the barriers being larger than those in the inversion pathway by more than 120 kJ mol(-1). Activation strain model analyses show that a higher deformation energy and a weaker interaction between deformed reactants lead to higher overall barriers in the reactions of NMe(2)Cl than those in the reactions of NH(2)Cl. Our studies on the reverse process of the title reactions suggest that the leaving ability of the anion in the gas phase anionic S(N)2@N reactions is mainly determined by the strength of the N-LG bond, which is related to the negative hyperconjugation inherent in NR(2)Nu (R = H, Me; Nu = HO, HS, HSe, NH(2), PH(2), AsH(2)).     

High-level direct-dynamics variational transition state theory calculations including multidimensional tunneling of the thermal rate constants, branching ratios, and kinetic isotope effects of the hydrogen abstraction reactions from methanol by atomic hydrogen

We report a detailed theoretical study of the hydrogen abstraction reaction from methanol by atomic hydrogen. The study includes the analysis of thermal rate constants, branching ratios, and kinetic isotope effects. Specifically, we have performed high-level computations at the MC3BB level together with direct dynamics calculations by canonical variational transition state theory (CVT) with the microcanonically optimized multidimensional tunneling (μOMT) transmission coefficient (CVT/μOMT) to study both the CH(3)OH+H→CH(2)OH+H(2) (R1) reaction and the CH(3)OH+H→CH(3)O+H(2) (R2) reaction. The CVT/μOMT calculations show that reaction R1 dominates in the whole range 298≤T (K)≤2500 and that anharmonic effects on the torsional mode about the C-O bond are important, mainly at high temperatures. The activation energy for the total reaction sum of R1 and R2 reactions changes substantially with temperature and, therefore, the use of straight-line Arrhenius plots is not valid. We recommend the use of new expressions for the total R1 + R2 reaction and for the R1 and R2 individual reactions.     

Deuterium kinetic isotope effects in gas-phase S(N)2 and E2 reactions: comparison of experiment and theory

The competition between bimolecular nucleophilc substitution and base-induced elimination is investigated through kinetic isotope effect measurements for gas-phase reactions of RCl + ClO- (R = methyl, ethyl, isopropyl, and tert-butyl) utilizing a FA-SIFT instrument. The overall reaction rate constants and the kinetic isotope effect for the reaction of C2H5Cl + ClO- are compared to computational results. [Hu, W. P.; Truhlar, D. G. J. Am. Chem. Soc. 1996, 118, 860.] Experimental results show that as the degree of substitution in the neutral reactant increases the E2 channel becomes dominant. The systematic change in the overall kinetic isotope effects indicates that, for the reaction of ClO- with C2H5Cl, both the SN2 and E2 pathways do occur, as predicted by computation; however the experimental reaction rate constants and KIE deviate strongly from the computational result.     

Thermal decomposition of model compound of algal biomass

This contribution investigates thermal decomposition of leucine, as a representative model compound for amino acids in algal biomass. We map out potential energy surface for a wide array of unimolecular and self-condensation reactions operating in the decomposition of leucine. Decarboxylation and dehydration of leucine ensues by eliminating CO₂ and –OH, respectively, from the –COOH group attached to the α-carbon. The molecular channel for deamination involves cleavage of NH₂ from α-carbon of leucine. The activation energies for direct elimination of CO₂, NH₃, and H₂O from a leucine molecule lie within 20.7 kJ/mol of each other. Activation energies for these decomposition pathways reside below the bond dissociation enthalpy of H–C(α) of 323.1 kJ/mol. The decarboxylation, deamination, and dehydration pathways, via radical-prompted pathways, systematically require lower energy barriers, in reference to closed-shell reaction corridors. Detailed computations at the CBS-QB3 level provide the Arrhenius rate parameters for the unimolecular and bimolecular reactions, and standard enthalpies of formation, standard entropies, and heat capacities for all the products and intermediates. A kinetic analysis of gas-phase reactions, within the context of a plug-flow reactor model, accounts qualitatively for the formation of major products observed experimentally in the thermal degradation of the condensed-phase leucine. Among notable N-containing species, the model predicts the prevailing of NH₃ over HCN and HNCO, in addition to corresponding appreciable concentrations of amines, imines, and nitriles. Our detailed kinetic investigation illustrates a negligible contribution of the self-condensation reactions of leucine in the gas phase.     

Collision-induced gas-phase reactions of perhalogenated closo-dodecaborate clusters--a comparative study

The gas phase reactivity of perhalogenated closo-dodecaborate clusters [B(12)X(12)](2-) (X = F, Cl, Br, I) with N-tetraalkylated ammonium counter ions was investigated by electrospray ionization ion trap mass spectrometry (ESI-IT-MS). Collisions with the background gases introduced a broad variety of gas phase reactions. This study represents the first experimental approach to a new class of boron-rich boron clusters that are not accessible in the condensed phase. The anionic ion pair [B(12)X(12) + N(C(n)H(2n+1))(4)](-) is generally found as the ion of highest mass. Its reaction sequence starts with an alkyl transfer from the ammonium ion to the dodecaborate cluster. Subsequently, the alkylated intermediate [B(12)X(12) + C(n)H(2n+1)](-) decomposes to give very reactive ions of the general formula [B(12)X(11)](-). These ions possess a free boron vertex and immediately bind to the residual gases N(2) and H(2)O in the ion trap by formation of the corresponding adducts [B(12)X(11) + N(2)](-) and [B(12)X(11) + H(2)O](-). Subsequent fragmentations of the water adduct repetitively substitute halogen atoms by hydroxyl groups. The fragmentation process of the free anion [B(12)X(12)](2-) depends on the applied excitation energy and on the halogen substituent X. A radical dehalogenation of the B(12) unit is observed for X = I, whereas for X = Cl or F the loss of small molecules (mainly BX(3)) dominates. The different reaction behavior is explained by the different electron affinity of the halogens and the strength of the boron-halogen-bonds. Surprisingly, isolation of the fragment ion [B(12)I(9)](-) in the ion trap yields the highly stable [B(24)I(18)](2-) dianion. This observation suggests a reaction between two negative ions in the gas phase.     

Theoretical Study of the Rate Coefficients for CH3NHNH2 + NO2 and Related Reactions

The kinetics and mechanisms of H atom abstraction reactions from CH₃NHNH₂ by NO₂ (R1) and related reactions have been investigated theoretically by using ωB97X‐D and CCSD(T)‐F12 quantum chemical calculations and the steady‐state unimolecular master equation analysis based on Rice–Ramsperger–Kassel–Marcus (RRKM) theory. For reaction (R1), both dissociation and isomerization steps between intermediate complexes were found to be important for the distribution of the dissociated bimolecular products. The dominant products of (R1) were found to be cis‐CH₃NHNH and HONO at lower temperature. The branching ratios for CH₃NNH₂ formation paths increased with increasing temperature. On the same reaction potential energy surface, six reactions including isomerization reactions between CH₃NNH₂ and cis‐/trans‐CH₃NHNH catalyzed by HONO were suggested to compete with the reverse reaction of (R1). The temperature‐ and pressure‐dependent rate expressions are proposed for kinetic modeling.