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Nitrous oxide (N2O) is an intermediate compound formed during catalysis occurring in automobile exhaust pipes. In this work, the N2O capture and activation by Pt and Pd atoms in the ground and excited states of many multiplicities are studied. Pt and Pd + N2O reactions are studied at multireference second-order perturbation level of theory using Cs symmetry. The PtN2O (1A′, 5A′, and 5A″) species are spontaneously created from excited states. Only the 5A′ and 5A″ states exhibit N2O activation reaction paths when N2O approaches Pt end-on by the N or O atoms side or side-on yielding NO or N2 as products, respectively. Pt+ cations ground and excited states, capture N2O, although only Pt+ (6A′ and 6A″) states show N2O activation yielding O and N2 as products. In the Pd atom case, PdN2O (1A′ and 5A″) species are also spontaneously created from excited states. The 5A″ state exhibits N2O activation yielding N2 + O as products. Pd+ cations in both ground and excited states capture N2O; however, only the [PdN2O]+ (4A′, 4A″, 6A′, and 6A″) states in side-on approaches and (6A′) in end-on approach activate the N2O and yield the N2 bounded to the metal and O as product. The results obtained in this work are discussed and compared with previous calculations of Rh and Au atoms. The reaction paths show a metal–gas dative covalent bonding character. Lowdin charge population analyses for Pt and Pd active states show a binding done through charge donation and retrodonation between the metals and N2O. © 2013 Wiley Periodicals, Inc.

This work shows that indigo's high stability can be attributed both to the large π conjugation inside the molecule and to intra- and intermolecular hydrogen bonds. The theoretical investigation of indigo's electronic structure has been performed using high-level methods. To understand the interactions in solid state, calculations of the dimer system with both molecules in the same plane was carried out. In the monomer, two intramolecular hydrogen bridges between amino and carbonyl groups occupy positions that would otherwise be the most reactive ones for nucleophilic and electrophilic attacks. In the dimer, amino and carbonyl groups on different monomers form intermolecular multicentred non-linear hydrogen bonds in six-member rings, protecting again the same reactive centres and explaining the limited solubility of indigo. The addition of the free radical OH breaks the central C = C double bond, the conjugation and the hydrogen bridges as a first step. The Gibbs energy calculation favours the addition of ...

In this work, the reaction of the atomic radicals H, O( 3 P), F and Cl with xylenes has been studied using ab initio theoretical methods. The stability of the isomeric adducts is analyzed and rules for the selectivity of addition of the different radicals are discussed. Ipso addition is found to be clearly favored for fluorine. In all cases, positions that are either ortho or ipso to a methyl group yield the most stable adducts, while carbon atoms that are in para positions with respect to the methyl groups seem to be the least susceptible of attack. These preferences contrast with normal addition rules for electrophilic reactants. Estimates of the enthalpy changes at 298 K for the reaction C 6 H 4 ( CH 3 ) 2 + X → C 6 H 4 ( CH 3 ) 2 X are determined for the first time. Values for Δ H r are compared with estimates obtained using Benson's additivity rules. They correlate very well with the atomic radius, the ionization potential, hardness and polarizability of the atoms.

Unrestricted Hartree-Fock calculations have been carried out to study the benzylperoxyl radical, an intermediate atmospheric contaminant. For this purpose, quantum mechanical MP2//UHF ab initio calculations were performed by using 6-31G∗∗ and 6-31 + G ∗∗ basis sets. Because no previous experimental nor theoretical data were available for benzylperoxyl, the results were compared with those of the smaller unsaturated peroxyl radicals, such as allylperoxyl. It is found that the calculated absolute minimal energy corresponds to a trans conformation in which the OO bond is sticking away from the benzene ring. Benzylperoxyl is found also to exhibit an unusually OO small bond order, which reflects the weakness of the bond, i.e. its ability to react with NO forming NO2 and subsequently ozone. A peculiar MO diagram is obtained, with the unpaired MO deeply located in the “doubly” occupied MO space. This effect is also observed in allylperoxyl. Structural parameters, charges, spin densities and dipole moments are also reported.