Role of Radical Elimination Reactions with Concerted Fragmentation in the Chain Decomposition of Alkyl Nitrates

The reactions X? + HCR₂ONO₂ → XH + R₂C=O + ?NO₂ are very exothermic due to the cleavage of the weak N?O bond and the formation of the energy-intensive C=O bond. The quantum chemical calculation of the transition state of these reactions for X? = Et? and EtO? used as examples showed that they actually proceed in one elementary act as eliminations with concerted fragmentation. The kinetic parameters were estimated within the framework of the intersecting parabolas model; the parameters allow the calculation of the activation energy and rate constant from the enthalpy of the above reaction. For a series of reactions involving the Et?, EtO?, RO?₂, and ?NO₂ radicals, on the one hand, and a number of alkyl nitrates, on the other, their enthalpies, activation energies, and rate constants were calculated. Based on the data obtained, new kinetic schemes of the chain decomposition of alkyl nitrates involving eliminations with fragmentation were proposed.