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Hybrid and double-hybrid density functionals are employed to explore the O–NO bond dissociation mechanism of vinyl nitrite (CH2=CHONO) into vinoxy (CH2=CHO) and nitric monoxide (NO). In contrast to previous investigations, which point out that the O–NO bond dissociation of vinyl nitrite is barrierless, our computational results clearly reveal that a kinetic barrier (first-order saddle point) in the O–NO bond dissociation is involved. Furthermore, a radical–radical adduct is recommended to be present on the dissociation path. The activation and reaction enthalpies at 298.15 K for the vinyl nitrite dissociation are calculated to be 91 and 75 kJ mol–1 at the M062X/MG3S level, respectively, and the calculated reaction enthalpy compares very well with the experimental result of 76.58 kJ mol–1. The M062X/MG3S reaction energetics, gradient, Hessian, and geometries are used to estimate vinyl nitrite dissociation rates based on the multistructural canonical variational transition-state theory including contributions from hindered rotations and multidimensional small-curvature tunneling at temperatures from 200 to 3000 K, and the rate constant results are fitted to the four-parameter Arrhenius expression of 4.2 × 109 (T/300)4.3 exp[−87.5(T – 32.6)/(T2 + 32.62)] s–1.

Thermodynamic properties of the methylmethoxy (CH 3 OCH 2 ) radical relevant to the pyrolysis and combustion of dimethyl ether are presented from quantum chemical calculations. The potential energy surface with torsional coordinates of the methyl and methylene groups of CH 3 OCH 2 is obtained at the CCSD(T)/aug-cc-pVTZ// B2PLYP/TZVP level. Internal rotations in the CH 3 OCH 2 geometry are found to generate two structures which are nonsuperposable mirror images, and a "double-well" feature is observed on the one-dimensional potential of the methylene rotation. Using the resulting torsional potentials, multiple structure and torsional anharmonicitities of CH 3 OCH 2 are evaluated by the multistructural method to obtain conformationally averaged partition functions which then serve as a basis for calculations of thermochemical parameters. The thermodynamic properties C p o , S o , and H T − H 0 at 298 K for CH 3 OCH 2 are predicted to be 64.54 J K −1 mol −1 , 283.73 J K −1 mol −1 , and 14.34 kJ mol −1 , respectively. The computational method CCSD(T)/cc-pV(5,6)Z//B2PLYP/TZVP with isodesmic reactions determine Δ f H o 298 (CH 3 OCH 2 ) to be on average 1.97 ± 0.64 kJ mol −1 with anharmonic torsion included, and this value is predicted to be 1.72 ± 0.62 kJ mol −1 by the G4 method. Results from atomization energy calculations using the CCSD(T)/cc-pV(5,6)Z//B2PLYP/TZVP method yields an enthalpy of formation value of 4.14 kJ mol −1 . The isodesmic reaction scheme is found to give an enthalpy of formation more accurate than atomization energy approach.

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