Thermal Decomposition of Gas-Phase Bis(1,2,4-oxadiazole)bis(methylene) Dinitrate (BODN): A CCSD(T)-F12/DFT-Based Study of Reaction Pathways.

Electronic structure methods based on density functional theory and coupled-cluster theory were employed to characterize elementary steps for the gas-phase thermal decomposition of bis(1,2,4-oxadiazole)bis(methylene) dinitrate (BODN). As typically found for nitrate ester-functionalized compounds, NO and HONO eliminations were the most energetically favorable unimolecular paths for the parent molecule's decomposition. From there, sequences of unimolecular reactions for daughters of the initiation steps were postulated and characterized.

Correlated Molecular Orbital Theory Study of the Al + CO Reaction.

Density functional theory (DFT) and correlated molecular orbital electronic structure calculations were used to study the Al + CO → AlO + CO reaction on the electronic ground-state potential-energy surface (PES). Geometries were optimized using DFT (M11/jun-cc-pV(Q+d)Z) and more accurate energies were obtained using the composite Weizmann-1 theory with Brueckner doubles (W1BD). The results comprise the most complete, most systematic characterization of the Al + CO reaction surface to date and are based on consistent application of high-level methods for all stationary points identified.

MRMP2, CCSD(T), and DFT Calculations of the Isomerization Barriers for the Disrotatory and Conrotatory Isomerizations of 3-Aza-3-ium-dihydrobenzvalene, 3,4-Diaza-3-ium-dihydrobenzvalene, and 3,4-Diaza-diium-dihydrobenzvalene.

The isomerizations of 3-aza-3-ium-dihydrobenzvalene, 3,4-diaza-3-ium-dihydrobenzvalene, and 3,4-diaza-diium-dihydrobenzvalene to their respective cyclic-diene products were studied using electronic structure methods with a multiconfigurational wave function and several single reference methods. Transition states for both the allowed (conrotatory) and forbidden (disrotatory) pathways were located. The conrotatory pathways of each structure all proceed through a cyclic intermediate with a trans double bond in the ring: this trans double bond destroys the aromatic stabilization of the π electrons due to poor orbital overlap between the cis and trans π bonds.

Isomerization barriers for the disrotatory and conrotatory isomerizations of 3-aza-benzvalene and 3,4-diaza-benzvalene to pyridine and pyridazine.

The isomerizations of 3-aza-benzvalene to pyridine and 3,4-diaza-benzvalene to pyridazine have been studied using ab initio methods with a multiconfigurational wavefunction. Transition states for both the allowed disrotatory and forbidden conrotatory pathways were located. The forbidden pathways proceed through an intermediate consisting of pyridine or pyridazine with a trans double bond in the ring: this trans double bond destroys the aromatic stabilization of the π electrons due to poor orbital overlap between the cis and trans π bonds.

Isomerization barriers and strain energies of selected dihydropyridines and pyrans with trans double bonds.

The stability of cis,trans-dihydropyridines and cis,trans-pyrans has been studied using ab initio methods. The strain introduced by the trans double bond has been determined relative to the cis,cis-isomers and introduces 58-69 kcal x mol(-1) of strain energy, at the G3 level of theory, depending on the particular isomer. Double bond rotation barriers have been calculated at the MRMP2/MCSCF level and range from 2.