Journal of Physical Organic Chemistry最新文献

Photochromic azobenzenes undergo light-mediated trans–cis isomerization. The cis isomer reverts to the trans isomer thermally. To investigate the effect of different monomer sequences on the thermal stability of cis-azobenzene, a series of copolymers, namely, block, and random structures containing stearic acid and azobenzene moieties as their side chains have been synthesized through reversible addition–fragmentation chain transfer (RAFT) polymerization. In this study, we investigate the photoisomerization of the trans and cis forms of the polymers and also the thermal reversal of the cis-azobenzene photochromic systems. The isomerization data revealed significant differences in the isomerization timescales between the polymers and the corresponding monomer. It was observed that the local polarity around the azobenzene units within a polymer was significantly influenced by the chain segment depending on whether it was in the vicinity of the hydrophobic alkyl chains or other azobenzene units. This local environment of the azobenzene units regulates the stabilization of the transition states during the cis–trans thermal isomerization, consequently affecting the half-life of the cis isomer.

Quantum chemical simulations were conducted to elucidate the electronic structure of the 2-azaallenyl radical cation, a key intermediate in several [3 + 2]-cycloadditions initiated by the oxidation of 2H-azirine. We propose one additional Lewis structure in resonance with the commonly accepted two Lewis structures for the model system of 1,3-diphenyl-2-azaallenyl radical cation, drawn from comprehensive theoretical data including molecular shape, bond order analysis, partial atomic charges, and spin densities. In addition to the ground state chemistry, the chemical structure of excited state species can be also understood with these three Lewis structures. Theoretical data imply that a newly suggested one mainly accounts for the ground state structure, and the excited state structure is better represented by the previously reported ones. Our claim is further bolstered by the prediction of the excited state geometries of the dicationic and neutral species. This research presents the extended set of Lewis structures for a better understanding electronic structure of 2-azaallenyl radical cation.

The mechanism of Ag₂CO₃-catalyzed reactions of acetonitrile, olefins, and amines was investigated by using the M06-L-D3/6-311 + G(d,p) method and level, and solvation model based on solute electron density (SMD) model was applied to simulate the solvent effect. Calculations show that the Ag₂CO₃ could achieve the Csp³-H activation by coordinating with the terminal nitrogen atom of CH₃CN; then, the addition reaction happened between the obtained Ag-complex intermediate and olefin via the coordination of Ag and benzene ring; finally, the obtained radical intermediate continues to go through one single electron transfer (SET) process, addition reaction, and H-shift reaction to yield the final product. The computational results reveal that Fe³⁺ cation would have assisted the SET process successfully and the path of direct addition with the amine is the optimal. Fukui function and dual descriptor can be used to predict the reactive sites, and electron spin density isosurface graphs can analyze the structures and reveal the substances.

An energetic material methyl urotropine perchlorate (MUTP) was synthesized from urotropine, perchloric acid, and triethylenediamine. The single crystal structure of the energetic salt was characterized by X-ray single crystal diffractometer. The results show that the single crystal of MUTP is an orthogonal crystal system with Pnma space group. The thermal decomposition process of MUTP was studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) technology. There were two exothermic peaks in TGA and DSC test, and the peak temperatures (T_p) were 261.61°C and 366.75°C, respectively. The thermal stability of MUTP was up to 247.10°C. Geometric optimization, frontier molecular orbitals, electrostatic potential (ESP), and weak interaction were explored by density functional theory using Gaussian 16. It is found that MUTP has a large energy gap (5.94 eV), which is larger than that of HMX (5.84 eV). The results of reduced density gradient method show that there are dense hydrogen bond interactions in MUTP with high electron density and intensity. In addition, a strong spatial repulsion is formed at the center of the cage.

Three new copper(II) mononuclear complexes containing different organoselenium groups (1–3) were synthesized and characterized by the following techniques: elemental analysis, IR and UV-Vis spectroscopies, electrochemical and conductimetric analysis, and mass spectrometry. Three new complexes, with substituents made in the para position of the aromatic portion of the N,N-bis(2-(phenylselanyl)ethyl)amine ligand: p-OCH₃ (1), p-CH₃ (2), and p-Cl (3), were synthetized to compare with the already published complex (4), with no substituents. The ligand coordinates to the copper(II) center in a tridentate way with Se, N, Se as donor atoms. The hydrolytic activity in phosphate diester cleavage of the complexes was investigated using 2,4-BDNPP as substrate. The modifications in the ligand are reflected in the difference between the catalytic and activation parameters, where the k_cat values follow the order: 4 > 2 > 3 > 1.

The subject of keto-enol equilibrium has a long history and well-established position within physical organic chemistry. Nonetheless, one still finds numerous reports of confusing findings and questions of accuracy when dealing with its practical application. In this report, some apparently anomalous recent observations are reviewed and then reexamined using density functional theory computations and agent-based (cellular automata) models of the keto-enol-anion equilibrium system. It becomes apparent that a resolution of many of the results can be achieved by taking into account the fact that although the ketone form is often present in overwhelmingly greater concentration, the enol can still contribute significantly to formation of the anion through its much greater acidity. Thus, in these cases, dissociation data assigned solely to the ketone form should in fact be recognized as representing a mixture of contributions from both the keto and the (neglected) enol form.

We have investigated the structural and thermodynamic parameters of group-14 substituted germylenes and their reactivity toward the H₂ molecule using density functional theory (DFT). We conducted the detailed Kohn–Sham molecular orbital (KS-MO) analysis to quantify the effective factors behind the increased reactivity of germylenes in going from C to Sn as substituents. The quantum theory of atoms in molecules (QTAIM), non-covalent interaction (NCI), and natural bond orbital (NBO) analyses revealed the nature of bonds and interactions and demonstrated the reactivity trend of germylenes in the presence of H₂. The results showed that in going from C to Sn, the reactivity increased due to an improvement in $�\sigma$-donation interaction between the filled lone-pair orbital of the germylene (LP_Ge) and the $�\sigma$*-orbital of H₂, which decreased the reaction barrier ($�∆$E^‡). As the germylene substitution was varied from C to Sn, a significant reactivity was observed for the germylene toward the H₂. This observation was caused by a reduction in steric repulsion between the germylene and the H₂ and less activation energy due to the higher $�\sigma$-donation and lower back-donation. We have presented the reactivity of new and rationally designed germylenes toward H₂ using various analyses that will serve as a guide for the activation of small molecules such as H₂, which is employed in many subsequent reactions.

In this study, we have developed a series of eight non-fullerene acceptors, constituting A-D-A type small molecules named (SS1–SS8) to enlighten the open-circuit voltage (V_oc) and the efficacy of pre-existed SR (reference) molecule. Density functional theory has been adopted to computationally assess the optoelectronic features of fabricated molecules with the B3LYP/6-31G (d, p) level of theory. Several factors like charge transfer, light absorption, binding energy, dipole moment, and reorganization energy are studied. The frontier orbitals analysis revealed that all the newly developed molecules have less bandgap (ranging from 1.97 to 2.22 eV) than SR (2.23 eV). Similarly, these newly engineered molecules also revealed better light absorption by screening remarkable redshift from 676.23 to 789.28 nm than SR (673.83 nm) in chloroform. These molecules have remarkably reduced excitation energy ranging from 1.71 to 1.83 eV than SR 1.84 eV. The exclusive CT analysis is carried out via J61:SS8 complex because of the higher V_oc of SS8 (acceptor). Additionally, SS8 has shown the least energy loss, making it a strong contender to be used to develop improved OSCs. Because of the exceptionally improved characteristics, these newly engineered molecules (especially SS8) can be considered potential aspirants for fabricating proficient OSCs.

On the basis of the density functional theory (DFT), the process of cycloaddition reaction of diazocarbonyl compounds with enones without leaving groups to obtain pyrazoles was proposed. First, the diazocarbonyl compounds reacted with enones to offer the intermediates by cycloaddition reaction, which was captured of hydrogen of the intermediate by the base to offer the nonaromatic pyrazole intermediate, which then give the final product by oxidation and isomerization in the air. This protocol corrected the reaction mechanism that was proposed in the experimental section. The negative correlation between the yields of products with the charges of ADCH at the C1 position of enones was also founded, which was consistent with the experimental results. The protocol could provide theoretical guidance for designing more efficient cycloaddition reaction.

One colorimetric and one fluorescent-indicator displacement assay (IDA) were studied to assess their interaction with methyl viologen (MV), an herbicide commercially known as paraquat. The host–guest complexes formed by cucurbit[7]uril (CB[7]) and the 4-nitroaniline (NA) or Berberine (Be) dyes function as colorimetric- and fluorescent-IDA for MV, respectively. The CB[7]@NA and CB[7]@Be complexes were characterized by UV–vis, fluorescence spectroscopy, and dynamic simulations. Isothermal titration calorimetry (ITC) experiments and dynamic simulations were employed to obtain thermodynamic data for the formation of the 1:1 inclusion complexes. Finally, NA is proposed as a reference colorimetric dye for determining CB[7]-binding affinities using competitive host–guest titrations, and the fluorescent-IDA as the best assay proposed, as it exhibits a high binding constant, a good detection limit of 2.7 × 10⁻⁶ mol L^-1, good linearity in the range from 4 × 10⁻⁶ mol L^-1 to 3.5 × 10⁻⁵ mol L^-1, in aqueous solution.