0000000000020207
AUTHOR
Víctor M. Ramírez-ramírez
Fate of several hydroxyalkyl isoprene radicals: Formation of hydroxycarbonyl compounds
Abstract The fate of two hydroxyalkyl radicals derived from the oxidation of isoprene with OH radical, resulting in the formation of two hydroxycarbonyls, was investigated by means of theoretical quantum chemistry methods. All the stationary points were optimised at the UMP2/6-31G(d) level, and high-level ab initio calculations were performed at the QCISD(T)/6-31G(d) level of computation upon MP2 optimised structures in order to refine the energy of the molecules characterised. Our results show that the reaction of hydroxyalkyl radicals with O 2 is a very favoured pathway that explains the formation of the two hydroxycarbonyls optimised.
Ab initio study on the mechanism of the HCO+O2→HO2+CO reaction
Abstract The gas-phase reaction HCO+O 2 →CO+HO 2 has been investigated by means of ab initio calculations. The mechanism can proceed through either a direct hydrogen abstraction or addition of O 2 to the formyl radical. The energy barriers calculated at the QCISD(T)/6-311G(2df,2p) level of theory upon QCISD/6-311G(d,p) optimized structures are, respectively, of 2.98 kcal mol −1 for the direct abstraction and of 2.26 kcal mol −1 for the addition. Thus, the results obtained show that there is not a dominant pathway in the HCO+O 2 reaction under atmospheric conditions of temperature and pressure.
Theoretical study of the OH addition to the endocyclic and exocyclic double bonds of the d-limonene
Abstract The initial step of the d-limonene + OH gas-phase reaction mechanism was investigated by means of ab initio calculations. We have considered eight different possibilities for the OH addition, corresponding to the two C–C double bonds, the two C atoms of each double bond, and the syn or anti orientation, with respect to the isopropenyl group (endocyclic attack) or the ring cycle (exocyclic attack). Activation energies calculated at the QCISD(T)/6-31G(d)//UMP2/6-31G(d) level, show that there are preferred orientations for the OH addition under atmospheric conditions of temperature and pressure.
A theoreticalab initiostudy on the H2NO + O3reaction
The deviation of the NH2 pseudo-first-order decay Arrhenius plots of the NH2 + O3 reaction at high ozone pressures measured by experimentalists, has been attributed to the regeneration of NH2 radicals due to the subsequent reactions of the products of this reaction with ozone. Although these products have not yet been characterized experimentally, the radical H2NO has been postulated, because it can regenerate NH2 radicals through the reactions: H2NO + O3 NH2 + O2 and H2NO + O3 HNO + OH + O2. With the purpose of providing a reasonable explanation from a theoretical point of view to the kinetic observed behaviour of the NH2 + O3 system, we have carried ab initio electronic structure calculat…
Theoretical study of the OH addition to the β-pinene
The initial step of the mechanism of the OH + β-pinene gas-phase reaction was investigated by means of ab initio calculations. Four different possibilities for the OH addition to the double bond are discussed, corresponding to the addition on each C atom of the double bond, and for each one, either the syn or anti OH attack to the two methyl groups on the (bi)cyclic molecule. Energy barriers calculated at the QCISD(T)/6-31G(d) level of theory on UMP2/6-31G(d) optimised structures, show that there are preferred orientations for the OH addition under atmospheric conditions of temperature and pressure.
Theoretical study of the formation reaction of the methyl vinyl ketone: A conformational approach
The formation reaction of both isomers of the methyl vinyl ketone (MVK) from the corresponding alkoxy radicals was investigated by means of theoretical methods based on quantum chemistry. Perturbative unrestricted Moller–Plesset (UMP2) and density functional methods B3LYP and BH and HLYP were used to obtain the stationary points on the potential energy surface. In addition to this, the interconversion reaction between both isomers of the MVK was studied, characterizing the corresponding transition state. A conformational study was done, and the energy and geometry of the stationary points located were analyzed by means of ab initio calculations. © 2005 Wiley Periodicals, Inc. Int J Quantum …