RRKM model of C2H4 dissociation: Heat of formation of vinylidene

Extended ab initio studies of the vinylidene–acetylene rearrangement

“…5 Also, an RRKM analysis of shock tube data yielded a heat of isomerization of 44Ϯ2 kcal/mol. 6 All these data are mutually consistent, but disagree with a value of 66 kcal/mol estimated from bond additivity. 15 The erroneous estimation by bond additivity implies that the bonding nature of vinylidene is different from the conventional arguments of bond order.…”

“…Vinylidene [1][2] has long been proposed as an intermediate in many chemical reactions and been studied extensively both experimentally [3][4][5][6] and theoretically. [7][8][9][10][11] Most of the earlier studies addressed the fundamental issue of whether vinylidene is a true intermediate or a saddle point on the C 2 H 2 potential energy surface.…”

A new mechanism for initiation of free‐radical chain reactions during high‐temperature, homogeneous oxidation of unsaturated hydrocarbons: Ethylene, propyne, and allene

“…Its basic feature includes the formation of a singlet carbene biradical from the isomerization of an unsaturated fuel molecule via 1,2-H shift (H-atom pseudorotation) [7] or in the case of alkene compounds from 1,1-H 2 elimination [8]. The carbene species then reacts with molecular oxygen to yield the initial radical pool.…”

“…This uncertainty, however, does not affect our conclusion concerning the importance of singlet carbene species in radical chain initiation as will be discussed later. There is no direct experimental kinetic data available for reactions (7) and (8). Here we assigned the rate constant for the back reactions to be k −7 = k −8 = 3 × 10 11 cm 3 mol −1 s −1 , based on the rate constants of analogous reaction (2) and C 2 H 5 + HO 2 → C 2 H 6 + O 2 .…”

Minor processes in the photolysis of azomethane at low pressure: An upper limit for the rate of the unimolecular elimination of H2 from vibrationally excited ethane

“…More recently, however, Pople et al [3], by ab initio calculations, predicted much higher barriers, 122 and 125 kcal mol-', respectively, for the 1,2-elimination of H2 from ethane and ethylene respectively, but found substantially lower barriers, 106.5 and 93.4 kcal mol-', respectively, for the 1,l-elimination. Elimination of H2 from ethylene (unspecified) is well established as the major channel in the unimolecular decomposition in IRMPD studies [4] and in shock tubes [5] where a n activation energy in the high pressure limit of 85 kcal mol-I has been estimated. Molecular elimination of H2 has never *To whom correspondence should be addressed.…”