Journal of Physical Organic Chemistry最新文献

In the current paper, the adiabatic ionization potentials (AIP) for 29 hydantoin derivatives and hydantoin-based drugs such as allantoin, phenytoin, mephenytoin, nilutamide, iprodione, nitrofurantoin, and ethotoin were calculated using the double hybrid ωB97XD density functional theory (DFT) in coupling with 6-311+G(2df,2p) basis set at the B3LYP/6-31+G(d,p) optimized geometry. The neutral and cationic radicals of the examined species were firstly optimized using the B3LYP/6-31+G(d,p) level. Final energies were improved by single point calculation using 16 different DFT methods such as B3LYP, ωB97, B97D, TPSSTPSS, M06-2X, …, and so forth, with 6-311+G(2df,2p) basis. Statistical tools such as root mean square error (RMSE) was used to examine the accuracy of the DFT method with respect to the standard reference AIP values. These standard references were calculated, for 12 hydantoin derivatives with less than nine non-hydrogen atoms, by taking the average values of the AIP computed using the G4, G3B3, and CBS-QBS methods. The vertical ionization potentials (VIPs), the vertical electron affinity (VEA), and global quantum parameters such as electrophilicity and nucleophilicity of the 29 molecules were also calculated. Substitution effect on the AIP, VIP, VEA, fundamental gap, electrophilicity, and nucleophilicity of the species under probe was studied and discussed. The results reveal that substitution of electron withdrawing group (EWG) raises the AIP and VIP, electrophilicity, and the fundamental gap, while substitution of electron donating group (EDG) raises the VEA and the nucleophilicity. Furthermore, the condensed Fukui functions were used to identify the active centers for nucleophilic, electrophilic, and free radical attacks.

A select history of dichlorocarbene chemistry between 1950 and 2010 will be presented. This is not a comprehensive review; rather, it is a personal perspective on the contributions of two respected colleagues, the reactive intermediate that spanned their research efforts, and their important contributions to organic synthesis and mechanistic thinking.

As an organic molecule catalyst, N,N′,N″-trihydroxyisocyanuric acid can selectively catalyze the oxidation of the methyl group of waste 2,4,6-trinitrotoluene to generate 2,4,6-trinitrobenzoic acid. This reaction can avoid environmental pollution by inorganic heavy metal catalysts. In this study, four reaction stages of this catalytic reaction were designed and validated computationally at the M06-2X-D3ZERO/6-311G(d,p) level using the acetic acid solvent model. These validations include transition state searches, intrinsic reaction coordinate calculations, reactant and product optimizations, and frequency calculations. The final reaction network of 23 transition states shows that after N,N′,N″-trihydroxyisocyanuric acid activation and common reaction, the network bifurcates into two stages: alcohol to carboxylic acid and aldehyde to carboxylic acid. Although the former stage releases about 155 kcal/mol of Gibbs free energy, less than the 177 kcal/mol from the latter stage, the overall reaction equation shows that the pathway including former stage does not consume the catalytically active substance IM_T2, which saves the energy required for reactivation and is thus more favorable. Furthermore, the key transition states in the reaction network include bimolecular substitution reactions and proton-hopping transfer reactions. Analyses of their interaction region indicators and intrinsic reaction coordinate results demonstrate strong selectivity. Additionally, the energy barriers and heat releases of the latter are twice and 1.3 times greater than those of the former, respectively. In summary, this study elucidated two competitive reaction pathways and identified the more energetically favorable and selective pathway, and it provides useful insights for further optimization of industrial utilization of 2,4,6-trinitrotoluene.

The Diels–Alder cycloaddition of cyclopentadiene and nitroethene, the intramolecular cycloaddition between a diene and triene, and the Diels–Alder cycloaddition of 2-hydroxyacrolein with 1,3-butadiene involving post-transition-state bifurcation (PTSB) were studied. These cycloaddition reactions were investigated using quasi-classical trajectory (QCT), classical molecular dynamics (MD), ring-polymer molecular dynamics (RPMD) simulations, and supervised machine-learning binary classification techniques. Room-temperature dynamics simulations started from the ambimodal transition state (TS) using the QCT, classical MD, and RPMD methods presented similar dynamics. Binary classification revealed that the initial geometry displacement from the ambimodal TS for the Diels–Alder cycloaddition of cyclopentadiene and nitroethene contributed to the branching dynamics and that the initial momenta for the intramolecular cycloaddition between a diene and triene and the Diels–Alder cycloaddition of 2-hydroxyacrolein with 1,3-butadiene played a significant role in the bifurcation dynamics.

The mixed valence (MV) radical anions of several bis(dioxaborines) with aromatic bridges of different length were studied by Vis/NIR spectroscopy, cyclic voltammetry, and theoretical calculations. The phenyl-bridged (1), the biphenyl-bridged (2), and bithiophene-bridged (5) radical anions show intense low-energy intervalence bands with vibrational structure typical of charge delocalized mixed valence species in the range of solvents studied. However, by subtracting from the experimental spectra of 2⁻ in MeCN the fraction corresponding to the delocalized part (taken as the spectrum in tetrahydrofuran [THF]), we get a localized charge-transfer bands that show a significant cutoff effect at the low-energy side, as predicted by classical Marcus–Hush theory. In the radical anions with three aromatic rings on the bridge, the localization of the charge changes with solvent. These radicals are predominantly charge-localized in the high λ_S solvent MeCN, charge-delocalized in the low λ_S solvent THF, and show both type of intervalence bands in DMF. Experimental results and theoretical calculations show that the electronic coupling between dioxaborine units in these three-ring bridged radical anions increases with the number of thiophene rings on the bridge.

The microwave-assisted extraction of the main phenolic component of green coffee beans, chlorogenic acid (CGA), was carried out employing deep eutectic solvents based on choline chloride and five different hydrogen bond donors (HBD) in a 1:2 ratio. The best performance for the extraction process of CGA was reached by the mixtures of choline chloride/ethylene glycol and choline chloride/urea. To understand the various interactions between the phenolic compound and the two most efficient deep eutectic solvents, computational calculations were carried out at the density functional theory (DFT) level, as well as Atoms in Molecules (AIM) and Non-Covalent Interactions (NCIs) analyses. In that way, a variety of hydrogen bond types were found in every structure. Nevertheless, the CGA does not disrupt the hydrogen bond network established between ChCl and the HBD. Among the strongest interactions are those hydrogen bonds between the quinic acid moiety and the ethylene glycol or the urea. In addition, the thermochemistry of the formation of the two main deep eutectic solvents and their corresponding complexes with CGA was calculated, where the formation of urea-based structures was slightly more effective by ~3 kcal/mol.

Due to intrinsic fluorescence behavior, and the environment-dependent excited-state intramolecular proton transfer (ESIPT) process, makes special attention towards flavonoids for conducting photophysical study. The binding of fisetin, morin hydrate, and quercetin with macrocyclic molecule Cucurbit[7]urils (CB[7]) has been studied using different spectroscopic methods. The changes in the thermodynamic parameters during complex formation between the flavonoids with CB[7] are estimated by an isothermal titration calorimetry study. From the spectroscopic measurement, we have seen that in the presence of CB[7], flavonoids show the ESIPT process and the prototropic equilibrium is present between different forms of flavonoids. The isothermal titration calorimetry study shows that the complex formation between these flavonoids with CB[7] spontaneously takes place at room temperature, which is an endothermic process.

The potential energy surface (PES) for the reaction of ozone with dimethyl sulfide (DMS) was calculated at the CCSD(T)/6-311++G(3df,2pd)//M06-2X/6-311++G(d,p) levels of theory. Result shows that on the singlet PES the addition–elimination mechanism is dominant, and H-abstraction mechanism is less competitive. The major channel starts from the addition of ozone and DMS leading to a weak intermediate IM1, which decomposes subsequently to DMSO and ¹O₂ via a barrier around 38.8 kJ/mol. With a barrier of 64.0 kJ/mol, the formation of HO₃ + CH₃SCH₂ via H-abstraction mechanism is subdominant. Besides, DMSO + ¹O₂ can take place further reactions to produce several products. The substitution mechanism was located on the triplet PES, however, with a rather high barrier it is negligible. Furthermore, the rate constants for the two channels leading to DMSO + ¹O₂ and HO₃ + CH₃SCH₂ were calculated from 200 to 1000 K. The total rate constant is 1.13 × 10^-20 cm³·molecule^-1·s^-1 at 298 K and 1 atm, in good agreement with previous experimental data. The overall rate constants are positive temperature dependent in the whole temperature range.