Quantum chemical studies of azoles 3. Thermodynamic stabilities of neutral molecules and intermediates formed in electrophilic substitution of azoles containing three or four heteroatoms

Density functional theory quantum chemical calculations of thermodynamic stabilities in the gas phase and in water were carried out for 1,3,4-oxadiazole and 1,3,4-thiadiazole, 1,2,4-1H-triazole and 1,2,4-4H-triazole, 1,2,3,4-1H-tetrazole and 1,2,3,4-2H-tetrazole molecules, and for cationic and bipolar (carbenoid) intermediates formed by these molecules in electrophilic substitution reactions (with proton as model electrophile) and the results obtained are compared. Differences in the chemical behavior of pairs of isomeric 1H- and 4H-1,2,4-triazoles and 1H- and 2H-tetrazoles are analyzed.     

Quantum chemical study of ferrocene derivatives 2. Arylation reactions with aminophenols

Russian Chemical Bulletin - Using the Hartree–Fock approximation and within the framework of the density functional theory (DFT) with the B3LYP functional in the 3-21G basis we carried out...     

Quantum-chemical Investigations of Pyrimidinones-4. 1. Tautomerism of 2-Oxopyrimidinones-4

Semiempirical quantum-chemical calculations have been carried out of the molecules of 2-oxopyrimidinones-4. The geometry and electronic structures and the stabilities of the tautomeric forms have been analyzed.     

Quantum chemical study of ferrocene derivatives 1. Arylation reactions with aminobenzoic acids

Russian Chemical Bulletin - Quantum chemical calculations of arylation reactions of ferrocene with three aminobenzoic acid isomers were carried out. Based on the results of the calculations using...     

Quantum-chemical Studies of Pyrimidin-4-ones. 2. Stability in the Gas Phase of Tautomers of Pyrimidin-2,4-dione, 2-Thioxo-, 2-Selenoxo-, 2-Amino-, and 2-Acetylaminopyrimidin-4-ones, and Their 6-Methyl- and 6-Phenyl Derivatives

The relative stability in the gas phase and the most probable reaction centers for electrophilic attack for the tautomers of pyrimidin-2,4-dione, 2-thioxo-, 2-selenoxo-, 2-amino-, and 2-acetylaminopyrimidin-4-ones, and their 6-methyl- and 6-phenyl derivatives have been investigated on the basis of the results of quantum-chemical calculations, using the semi-empirical PM3 method, without taking solvent effects into account.     

Quantum chemical studies of pyrimidin-4-ones 3. 2-Oxo(thioxo,selenoxo)pyrimidin-4-ones and 5,6-dimethyl-2-oxo(thioxo)thieno[2,3-d]pyrimidin-4-ones

Quantum chemical calculations for 2-oxo-, 2-thioxo-, and 2-selenoxopyrimidin-4-ones, as well as for 5,6-dimethyl-2-oxo- and 5,6-dimethyl-2-thioxothieno[2,3-d]pyrimidin-4-ones, were carried out at the HF and DFT levels. An analysis of the relative energies shows that the 2-oxo form or the related thioxo or selenoxo forms are energetically more favorable in tautomeric interconversions of all the compounds under study both in the gas phase and in solutions in ethanol, acetonitrile, and DMSO.     

Quantum chemical studies of pyrimidin-4-ones Part 6. On peculiarities of the reactions with nitrating agents of some carboxylic acids of the thieno[2,3-<Emphasis Type="Italic">d</Emphasis>]pyrimidin-4-one series and their esters

Quantum chemical calculations of the energies, electronic structures, and molecular geometries of 5-methyl-, 2,5-dimethyl-, 3,5-dimethyl-, and 2,3,5-trimethyl-4-oxothieno[2,3-d]pyrimidine-6-carboxylic acids; 5-methyland 3,5-dimethyl-2,4-dioxothieno[2,3-d]pyrimidine6-carboxylic acids; 5-methyland 3,5-dimethyl-4-oxo-2-thiothieno[2,3-d]pyrimidine-6-carboxylic acids; and their ethyl esters were performed in terms of the HF and DFT (B3LYP) approximations in the 3-21G basis set. The reactions routes with nitrating agents were examined, and the factors governing the direction of the reactions, the probability of their occurrence were determined. Selective ipso-substitution of the 5-methyl group by the nitro group at the C(5) atom of the thiophene fragment is hindered for all compounds studied. The reasons for the unfavorable ipso-substitution were discussed taking into account effects of solvents and substituents in positions 2, 3, and 6 of 6-carboxyand 6-ethoxycarbonyl-substituted thieno[2,3-d]pyrimidin-4-ones.