Theoretical Study of the Formation of Benzofurotriazines by Reaction of 3-Substituted 1,2,4-Triazines and Fused Azolo[1,2,4]triazines with Resorcinol

3-Methylthio- and 3-amino-1,2,4-triazines react with resorcinol to give benzofurotetrahydrotriazine derivatives, while reactions of [1,2,4]triazolo[4,3-b]- and tetrazolo[1,5-b][1,2,4]triazines with resorcinol stop at the stage of resorcinol addition. According to the results of quantum-chemical calculations, the possibility for further cyclization of the resorcinol addition products is determined by the following factors: tautomeric and conformational states of the compounds, which ensure spatial proximity of the hydroxy group to the cyclization center (C⁶); charges on the C⁶ atom of the triazine ring and oxygen atom of the resorcinol fragment in the conformation most favorable for cyclization; and energies of the highest occupied and lowest unoccupied molecular orbitals of the resorcinol addition products.     

Changes in the vibrational characteristics of substituted 1,2,4,5-tetrazines after complexation with 1,2,3-benzotriazole: A theoretical study

The complexation of 3,6-substituted 1,2,4,5-tetrazines with benzotriazole was studied theoretically based on the vibrational spectra. For model complexes, the energy was minimized by the geometrical parameters, and the spectral characteristics were calculated by the PM3 method. The shift of the bond vibration frequencies of the atoms involved in complexation after the formation of different various intermolecular contacts was determined. This made it possible to determine the type of intermolecular interaction and suggest the structures of the complexes.     

Comparison of non-covalent interactions and spectral properties in 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium mono- and tetraiodide crystals

The reaction of 1-methyl-3-methylthio-5-phenyl-1,2,4-triazinium (MTPT) iodide with diiodine in a solution leads to monoiodide crystal structure that in excess of iodine gives the unusual tetraiodide anion with two central iodine atoms in disorder. The bonding within the anion has been characterized as I^–…I₂…I^–; the existence of the bound iodine molecule inside has been proven by the characteristic band in experimental and calculated Raman spectra. Non-covalent interactions of MTPT in considered crystal structures are different. Monoiodide anion as a strong electron donor allows the formation of the S…I chalcogen bonds that are absent in tetraiodide structure. The features of halogen bonds within the I₄^2– anion are also performed.

     

A quantum topological study of the electron density in monomers and dimers of acyclic azathiens with aromatic substituents

A theoretical study of electron density, ρ(r), and the Laplacian (ab initio, DFT B3LYP/6-31G(d, p) basis set) has been carried out for nine molecules of azathiens with aryl substituents (Ar-N=S=N-Ar₁) and for sixteen dimers corresponding to typical arrangements of neighboring molecules in the crystal structures of Ar-N=S=N-Ar₁. A dependence was established of the values of the electron density at (3, ?1) critical points in the area of inter-stack and intra-stack atom-atom contacts on the internuclear distance.     

Atoms-in-molecules study of intra- and intermolecular bonding in the pentaerythritol tetranitrate crystal

Chemical bonding in the pentaerythritol tetranitrate crystal based on the experimental electron density obtained from X-ray diffraction data at 100 K and theoretical calculations at the experimental molecular geometry have been analyzed in terms of the Quantum Theory of Atoms in Molecules. Features of the intra- and intermolecular bond critical points and the oxygen atom lone-pair locations are discussed. Numerous intermolecular bonding interactions, including O...H and O...O, have been found and characterized. Atomic charges and atomic energies were integrated and compared with those for similar compounds. The N-O topological bond orders have been calculated for the first time, and the PETN atomic valences have been estimated.