Investigation of the π–π stacking interactions without direct electrostatic effects of substituents: the aromatic∥aromatic and aromatic∥anti-aromatic complexes

Stability of the π–π stacking interactions in the ben∥substituted-ben and ben∥substituted-COT complexes was studied using the computational quantum chemistry methods (where ben and COT are benzene and cyclooctatetraene, ∥ denotes π–π stacking interaction, substituted-ben and substituted-COT are benzene and cyclooctatetraene which substituted with four ethynyl-X groups, respectively, and X = OH, CH₃, H, F, CF₃, CN and NO₂). In these complexes electron-withdrawing substituents lead to larger binding energies and electron-donating ones lead to weaker interactions compared to X = H. There are meaningful correlations between the Hammett constants and binding energies. The atoms in molecules (AIM) analysis shows that formation of these complexes is accompanied by increase in the electron charge densities at the ring critical points of the substituted-ben and substituted-COT rings which leads to increase/decrease of the π–π stacking interactions in the ben∥substituted-ben/ben∥substituted-COT complexes. The charge transfer occurs from benzene to substituted-ben in the ben∥substituted-ben complexes and from substituted-COT to benzene (with the exception of X = CN) in the ben∥substituted-COT ones. Nuclear magnetic resonance calculations demonstrate that interactions of the more aromatic substituted-ben/less anti-aromatic substituted-COT rings with benzene in the ben∥substituted-ben/ben∥substituted-COT complexes can be helpful to enhance strength of the π–π stacking interactions. Thus, regardless of ring size, the π–π stacking interaction is an aromatic–aromatic interaction and π electron cloud properties of interacting rings affect on the strength of this interaction.     

Synthesis of pyrazine-2,3-dicarbonitriles via the one-pot three-component reaction of 4-benzoyl-5-phenylamino-2,3-dihydrothiophene-2,3-dione,diaminomaleonitrile, and functionalized alcohols in acetonitrile

An efficient one-pot three-component reaction of 4-benzoyl-5-phenylamino-2,3-dihydrothiophene-2,3-dione, diaminomaleonitrile, and alcohols with hetero-atom substituents or several hydroxyl groups in acetonitrile solvent under reflux led to the formation of 5-(2-substituted ethoxy or propoxy-2-phenyl-1-N-phenylthiocarbamoylethenyl)-6-oxo-1,6-dihydropyrazine-2,3-dicarbonitrile derivatives in good yields.     

Economical synthesis of nanocrystalline alumina using an environmentally low-cost binder

Sol-gel, a commonly used technique, involves the formation of an amorphous gel from a precursor solution. In this research nanocrystalline alumina powders have been synthesized through a new sol-gel simplified method. The route involved using an environmentally low-cost binder and aluminum nitrate in an aqueous medium. The added metal ions were dispersed in the gelled binder matrix. The gelled mass was dried and characterized by simultaneous thermogravimetric and differential thermal analysis (TG-DTA) and calcined at 350, 400, 530, 650, and 900 °C for 2 h. The samples were evaluated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The used binder can be applied to form a perfect matrix for the entrapment of metal ions that during heat treatment, gives rise to ultrafine amorphous or crystalline alumina particles. In this study, the transition phases of alumina with particle sizes of 15-25 nm as well as aluminum oxide hydrate phase were produced by the heat treatment of the gelled mass at temperature 650 °C. By increasing the calcinations temperature to 900 °C, alumina transition phases were changed and aluminum oxide hydrate eliminated. The particle sizes at this temperature were obtained in the range 15-30 nm. The particle size and crystallite size of products measured from XRD and TEM were in good agreement.