Electrochemical Oxidation of Catechols in the Presence of Triethyl Phosphite

The mechanism of electrochemical oxidation of catechol and some of its derivatives have been studied in the presence of triethyl phosphite as a nucleophile in aqueous solution. Voltammetric studies indicate that the quinones derived from catechol, and its derivatives, participate in Michael addition reaction with triethyl phosphite. The reaction mechanism consists of electron transfer followed by a chemical reaction which is named as an EC mechanism. The homogeneous rate constants (k_obs) were estimated by comparing the experimental cyclic voltammograms with the digitally simulated voltammograms based on EC mechanism. Also the effects of nucleophile concentration and substituted group of catechols on voltammetric behavior and the rate constants of chemical reactions were examined.     

Efficient Routes for the Synthesis of Dinaphthosulfide (BINOL Derivatives) and Dibenzosulfide Aza Podands Containing Ethanolamine

Four new dinaphthosulfide and dibenzosulfide aza podands were synthesized. The synthesis of these podands was performed under three different reaction conditions: 1) diester, K ₂ CO ₃ , methanol, and RT; 2) diester, ethanolamine, and microwave (MW); and 3) diacid dichloride, ethanolamine, Et ₃ N, CH ₂ Cl ₂ , RT. Two kinds of diester (dinaphthosulfide and dibenzosulfide) were used for the preparation of dihydroxy podands. These dihydroxy podands were reacted with thionyl chloride to afford dichloro podands. The second route gave excellent yields of dihydroxy podands. Dichloro podands are more soluble than dihydroxy podands in conventional solvents such as methanol, chloroform, and acetonitrile.     

Synthesis of New 1,4-Dihydropyridine Derivatives Containing Thiazolyl Substituents

A series of 4-[2-methyl (or aryl) thiazole-4-yl]-2,6-dimethyl-3,5-diacetyl (or dibenzoyl) 1,4-dihydropyridines were synthesized using a modified Hantzsch reaction involving the condensation of the corresponding aldehyde with acetyl acetone or benzoyl acetone. The preparation of the corresponding aldehydes (2-methylthiazole-4-carboxaldehyde and some 2-arylthiazole-4-carboxaldehydes) was achieved by a simplified protocol of the published synthesis.     

Synthesis of a Novel Heterocyclic System, [1,2,4] Triazino[1,2-a]Pyrimido [4,5-e] [1,3,4] Thiadiazines

Substituted 6-chloro-pyrimido[4,5-e][1,3,4] thiadiazine was converted to the corresponding 6-hydrazino derivative by treatment with hydrazine hydrate in DMF/Et ₃ N. The latter was converted to various substituted [1,2,4]triazino[1,2-a] pyrimido[4,5-e][1,3,4]thiadiazines.     

A Practical and Eco-Friendly Method for Conversion of Epoxides to Thiiranes with Immobilized Thiourea on CaCO3

Abstract

Solvent-free conversion of various epoxides to the corresponding thiiranes was carried out efficiently with immobilized thiourea on CaCO₃. The reactions were completed within 1–12 min under oil bath (60 °C–70 °C) conditions to afford thiiranes in 88%–98% yields.

[Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements for the following free supplemental resource: Figures S1–S3.]

GRAPHICAL ABSTRACT      

A DFT study on carbon-doping at different sites of (8, 0) boron nitride nanotube

A density functional theory study is carried out to investigate the geometries and electronic structure of pristine and carbon-doped (8, 0) single-walled boron nitride nanotubes (BNNTs). In order to understand the effect of impurities or doping on (8, 0) single-walled BNNT, we simulated C-doping in six different ways. Geometry optimizations reveal that in the considered models, B–N bond lengths are not significantly influenced by C-doping. Based on the quantum theory of atoms in molecules analysis, charge density accumulation for axial B–N bond critical points (BCPs) of pristine BNNT is slightly larger than zigzag ones. However, due to C-doping at the B- or N-tips, the evaluated electron density tends to decrease slightly at both axial and zigzag B–N BCPs. Besides, results indicate that influence of C-doping on properties of the (8, 0) BNNT could be also detected by values of chemical shielding isotropy (σ _iso) and anisotropy (Δσ).     

Quantitative analysis of intermolecular forces for hydrogen bond driven self-assembly of resorcinol and bis(pyridine) substituted ethylene cocrystals, before and after [2 + 2] dimerization

The long-range and dispersion corrected density functional theory (DFT + Disp), and Møller–Plesset second-order perturbation theory (MP2) were used for describing the intermolecular interactions between hydrogen bond driven self-assembly of 2(5-CN-res) … 2(4,4′-bpe) and 2(4,6-diCl-res) … 2(4,4′-bpe) cocrystals [where 5-CN-res = 5-cyanoresorcinol, 4,6-diCl-res = 4,6-dichlororesorcinol, and 4,4′-bpe = trans-1,2-bis(4-pyridyl)ethylene], before and after [2 + 2] dimerization to 2(5-CN-res) … (4,4′-tpcb) and 2(4,6-diCl-res) … (4,4′-tpcb), respectively [where 4,4′-tpcb = 1,2,3,4-tetra(4-pyridyl)cyclobutane]. The nature and strength of intermolecular forces were studied using the absolutely localized molecular orbitals energy decomposition analysis, and the plot of reduced density gradient versus the electron density multiplied by the sign of the second Hessian eigenvalue [sign(λ₂)ρ]. The results show that the interaction of 2(4,4′-bpe) is basically dispersive nature, while all of the electrostatic, dispersion, polarization and charge-transfer interactions are largely contributed to the interaction energy of 2(4,4′-bpe) with 5-CN-res and 4,6-diCl-res molecules. The total interaction energy of complexes before dimerization is greater than that after dimerization. Since the contribution of polarization and charge-transfer interactions after dimerization are nearly unchanged, the main difference in the interaction energy of complexes is due to the weaker contribution of van der Waals and electrostatic forces in the products.     

Ab initio and DFT studies on 1-(thionitrosomethylene) hydrazine: conformers, energies, and intramolecular hydrogen-bond strength

In the current study, we present an intramolecular HB, molecular structure, π-electrons delocalization and vibrational frequencies analysis of 25 possible conformers of 1-(thionitrosomethylene) hydrazine by means of DFT (B3LYP), MP2 methods in conjunction with the 6-311++G** and augmented correlation-consistent polarized-valence triple-zeta basis sets and G2MP2 theoretical level. The influence of the solvent on the stability order of conformers and the strength of intramolecular hydrogen-bonding was considered using the Tomasi’s polarized continuum model. Statistical analyses of quantitative definitions of aromaticity, nucleus independent chemical shift, harmonic oscillator model of aromaticity, aromatic fluctuation index, and the π-electron delocalization parameter (Q) as a geometrical indicator of a local aromaticity, evaluated for this conformers. Further verification of the obtained transition state structures were implemented via intrinsic reaction coordinate (IRC) analysis. Calculations of the ¹H NMR chemical shift at GIAO/B3LYP/6-311++G** levels of theory are also presented. The calculated highest occupied molecular orbital (MO) and lowest unoccupied MO energies show that charge transfer occur within the molecule. Hydrogen-bond energies for H-bonded conformers were obtained from Espinosa method and the natural bond orbital theory and the atoms in molecules theory were also applied to get a more precise insight into the nature of such H-bond interactions.     

The response of selected isomers of B80 buckyball toward NH3 adsorption: a density functional theory investigation

Density functional theory calculations at the B3LYP/6-31G(d) and B3LYP/6-31+G(d) levels were carried out for the adsorption of NH₃ on three symmetric isomers of B₈₀ {C ₁, T _h, I _h}. To investigate the binding features of B₈₀ isomers with NH₃, different studies including the structural and electronic parameters, the ¹⁴N electric field gradient tensors and the atoms in molecules (AIM) properties were considered. The calculated parameters by these investigations can be used as powerful tools to find out some of the unknown aspects of electronic structures of the boron buckyball and its isomers. According to previous studies, boron buckyball as an amphoteric and a hard molecule has two distinct reactive sites defined as cap and frame which act as an acid and a base, respectively. Regarding the obtained results in this study, all the isomers had the same exposure when NH₃ molecule reacted with the external wall of B₈₀. For instance, the stability of N–B bond in the cap site was significantly more than the stability of N–B bond in the frame. Moreover, the adsorption of NH₃ on frame site showed a considerable reduction in HOMO–LUMO energy gap. According to AIM theory, an electrostatic nature was observed for N–B interaction. Concerning the selected isomers of buckyball, the capability of the NH₃–B₈₀ complexes to localize electron at the N–B bond critical points depend on the reaction sites significantly. In general, ¹⁴N nuclear quadruple coupling constants and asymmetry parameter reveal a remarkable effect of NH₃ adsorption on electronic structure of the B₈₀.