Journal of Physical Organic Chemistry最新文献

Dicarboxylic acids (DCAs) are major players in the formation of secondary organic aerosols (SOAs) and climate change. DCAs have potential impact on human health and environmental issues ranging from local scale to global scale participate mainly in the cloud condensation. In this context, oxalic acid (OA) and malonic acid (MA) are the most dominant DCAs in the atmosphere. A full atmospheric degradation mechanism of OA and MA with the most reactive tropospheric oxidants, namely, OH, Cl and NO₃ radicals, were studied using M06-2X, ωB97XD/cc-pVTZ and 6-311++G(2df,2p) level of theories. To evaluate the atmospheric influence, this study enables us to deep investigation of fate of OA and MA with respect to the mentioned radicals and their subsequent secondary reactions. The latter result in the formation of carbon dioxide (CO₂), formic acid (HCOOH), which contributes to the formation of SOA and climate change. The reaction mechanism in this study was initiated through H-abstraction reaction, followed by dehydrogenation and decarboxylation reaction of both DCAs. The rate coefficients of OA, MA with OH, Cl and NO₃ radicals are determined theoretically using variational transition state theory (VTST) with Eckart tunnelling method in the temperature range of 278–1000 K. At 298 K, the rate coefficient of OA with OH, Cl and NO₃ are 2.48 × 10⁻¹⁵, 2.37 × 10⁻²⁰, 6.16 × 10⁻²³ in cm³ molecule⁻¹ s⁻¹, whereas MA with OH, Cl and NO₃ are 9.76 × 10⁻¹⁴, 1.01 × 10⁻¹² and 5.89 × 10⁻¹⁸ in cm³ molecule⁻¹ s⁻¹, respectively. Our present results shed light on the atmospheric implications of two DCAs and provide the significant insight for the atmospheric pathways.

In this study, the density functional M06-2X/6-311++G(3df,3pd) method was employed to investigate the mutual isomerization reaction mechanism of 5-chlorouracil from diketone to diol under the catalysis of water, methanol, formic acid, and an electric field. Parameters such as reaction enthalpy, activation energy, activation Gibbs free energy, and proton transfer reaction rate were obtained. The computational results show that under the same conditions, formic acid demonstrates the best catalytic effect, while the influence of electric field catalysis on the reaction barrier is minimal.

The reactivity of imidazole, pyrazole, 1,2,4-triazole, 1,2,3-triazole, and tetrazole with acetone (propan-2-one) has been studied by ¹H and ¹³C NMR using acetone-d₆ as solvent at temperatures ranging from 173 to 300 K at 10 K intervals. Simultaneously, the reaction has been theoretically calculated at the B3LYP/6-311++G(d,p) level, and experimental and theoretical results have been compared. The equilibrium constants between azoles and adducts α,α-dimethyl-azole-methanol were analyzed, assuming that the straight part of the plots –R ln K_e vs. 1/T can be used to determine ΔH and ΔS. Calculated and experimental data are related, but the theoretical values are proportionally higher. The tautomerism of triazoles and tetrazole has been considered in order to discuss the reactions.

6-Iodo-3-(triflamidomethyl)-4-triflyl-1,4,2,7-oxazadisilepane 1 and the product of its cyclization, 2,2,4,4-tetramethyl-6,8-bis (triflyl)-3-oxa-6,8-diaza-2,4-disilabicyclo[3.2.2]nonane 2, have been studied by gas-phase electron diffraction and DFT calculations. The conformational equilibrium in the gas phase was shown to include three and two conformers for 1 and 2, respectively, in contrast to only one conformer determined by single crystal X-ray diffraction. The structural analysis of the conformers was performed and the pathways of the conformational transitions were analyzed.

The potential energy surfaces for the reactions of 1,3-butadiene with 2-hydroxythioacrolein and 2-aminoacrolein exhibit ambimodal transition states leading to both dipolar (4 + 3) and Diels–Alder (4 + 2) cycloaddition products, thereby demonstrating a post transition state bifurcation feature. We have investigated the bifurcation dynamics of these reactions using three molecular dynamics (MD) methods: quasi-classical trajectory, classical MD, and ring-polymer MD simulations. The trajectory calculations were performed with the semiempirical GFN2-xTB method with the element-specific parameters optimized to reproduce the density-functional theory calculations. The effect of water solvation was examined using an implicit solvation model, revealing significant differences in bifurcation dynamic between gas-phase and solution-phase reactions. Nuclear quantum effects were found to play a crucial role in the proton-transfer process from the (4 + 3) intermediate to the (4 + 3) product in the case of the 2-aminoacrolein reaction.

This study aimed to evaluate the effect of supplementing different protease enzymes on growth performance, intestinal morphology, and selected carcass traits in broilers fed diets reduced 3.5% in crude protein (CP) and amino acids (AA). One thousand one-day-old Ross 308 broilers (41 g) were assigned to five dietary treatments with ten replicates of 20 birds each: a positive control (PC) diet formulated to meet Ross 308 AA requirements, a negative control (NC) diet reformulated to provide 3.5% lower CP and AA compared to PC, NC supplemented with a multi-protease (PR1) solution, containing 3 different coated proteases produced from Aspergillus niger, Bacillus subtilis and Bacillus licheniformis, NC supplemented with a serine protease (PR2) produced from Bacillus licheniformis, and NC supplemented with an alkaline protease (PR3) produced from Bacillus licheniformis. At slaughter, 40 birds per treatment were used to assess the effect of the different treatments on carcass traits. At 32 days, samples of the duodenum, jejunum, and ileum of 10 birds per treatment were collected for intestinal morphology evaluation. Birds fed PC and NC supplemented with multi-protease exhibited better (p < 0.05) feed efficiency compared to NC and NC supplemented with all the other protease enzymes. Multi-protease supplementation was linked to the highest (p < 0.05) carcass weight and yield. There were significant differences (p < 0.05) between treatments in all gut segments, with PC, PR1, PR2, and PR3 exhibiting longer villi height (VH) compared to NC. This study demonstrates that 3.5% reduction of CP and AA negatively affected for the overall period feed efficiency, carcass yield, and intestinal morphology. The supplementation of the multi-protease restored feed efficiency and improved carcass yield.

The desulfurization of carbons modified with SO₂ was studied as a dispersion in boiling cyclohexane (81°C) using activated carbon (mAC) and graphene oxide (mGO), modified by SO₂. The steady-state species in the carbon matrix after the catalytic reduction of SO₂ was considered a trisulfane. For mAC, there was a burst of a sulfur species identified as S₂ by UV spectrum with a maximum at 217 nm (ε_M at 217 nm = 2.56 × 10³) that showed a second-order decay of absorbance with $�k_{S_2}$ = 47.29 M^-1·sec^-1 ($�{\mathrm{\Delta G}}_{354}^{‡}$= 18.1 kcal·mol^-1). The product was postulated to be S₄. No other consecutive reaction was observed because of the possible adsorption of S₄ in the carbon matrix. The desulfurization of mGO was shown by XPS and the kinetics were a second-order decay up to 16 min ($�k_{S_2}�=$ 18.41 M^-1·sec^-1;$��{\mathrm{\Delta G}}_{354}^{‡}$= 18.8 kcal·mol^-1) followed by a second-order increase of absorbance with $�k_{S_4}$ = 3.84 M^-1·sec^-1 ($�{\mathrm{\Delta G}}_{354}^{‡}$= 19.9), where the product showed a double maximum at 260-285 nm typical of S₈. These results are consistent with a mechanism of consecutive thermodynamically favorable dimerizations of S₂ and S₄ and with the desulfurization mechanism that has been previously postulated.

The topological resonance energy (TRE) method was used to investigate the aromaticity of hetero[8]circulenes in both their neutral and doubly charged ion states. The compounds varying stabilities in different charged states were explained in terms of the topological charge stabilization rule. The TRE-based aromaticity indices were compared with those obtained by the gauge-including magnetically induced currents (GIMIC) method. However, the lack of correlation between the TRE and GIMIC aromaticity indices, as well as the contradictory trends observed, suggest that further investigation is necessary to fully understand the aromaticity of hetero[8]circulenes. We employed the circuit resonance energy (CRE) method to assess local aromaticity. Our CRE results indicate that individual benzene or heterocyclic five-membered units within the molecule maintain their strong aromatic character and serve as the primary source of global aromaticity, both in their neutral and doubly charged ion states. Although our CRE results provide valuable insights, it is important to note that there are cases where the magnitude of local aromaticity predicted by the nucleus-independent chemical shift (NICS[0] and NICS[1]) indices does not align with our CRE results.

The paper is devoted to the measurements of one-electron redox potentials of transient free radicals E^o. These values can be measured in the reversible redox reactions of radicals under investigation with a reference pair, which E^o is known. Several E^o of transient radicals are presented. The convenient and important objects for E^o measurement are quinone/semiquinone radical-anions. A general problem of measurement of thermodynamic properties of short-lived transients is discussed.

Structural aspects of single CC bond dissociation energies are examined and it is shown that in certain cases a negative bond dissociation energy (BDE) implies a very weak bond and an unstable species prone to bond breaking resulting in dissociation or structural rearrangement. It is proposed that, in such cases, a better quantitative indicator for the strength of the bond is the activation energy required for its fission. o-Phenelylene bis(nitrene) 1 is computed to have the most negative CC BDE for an observable species. Under cryogenic conditions, activation energy for the dissociation of this bond has been measured as only 2.8 kcal/mol, making it the weakest that we know of. An explanation based on the formation of two new bonds as responsible for this extremely weak bond is given.