Journal of Physical Organic Chemistry最新文献

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.

The design of organic solar cells, OSCs, requests a more efficient configuration of photoactive layers composed of p-type (quinoxaline, Qx) and n-type (naphthalene diimide, NDI) semiconductors that enable light harvesting along with a high-power conversion efficiency. Here, Qx-(phenyl or Ph) and NDI structures have been modulated using both electron withdrawing (EWG) and electron donating (EDG) groups such as −F, −NHCOCH₃, −OCH₃, −OH, −CHO, −COOCH₃, −COOH, −CN, −SO₃H, and −NO₂, aiming to design an effective photoactive p-n layer. The HOMO-LUMO gap of Qx-Ph can be tuned to the visible light spectrum by the addition of EWG in the Qx ring (decreasing the LUMO energy) and by EDG in the Ph ring (increasing the HOMO energy). The analyzed complexes show key electronic properties in organic solar cells with large power conversion efficiency. Descriptive data analysis suggests that the magnitude of the non-covalent interactions in donor$�\dots$ acceptor (D$�\dots$ A) complexes is expected to play a role in the efficiency of OSCs. The results will contribute to a more effective design of the photoactive layer in OSCs.

The study investigates the reactivity of a cyclic five-membered intramolecular P/B frustrated Lewis pair towards acrolein through a cycloaddition reaction. Intrinsic reaction coordinate (IRC) calculations suggest the single-step mechanism. It has been observed that the cycloaddition reaction occurs through a concerted mechanism in both the presence and absence of the catalyst. Analysis of reaction force and reaction electronic flux provides valuable information about the total work required and electronic activity along the IRC. Additionally, natural bonding orbital (NBO) analyses enrich the understanding of the mechanism in terms of the electron transfer process during the chemical reaction.

Hydrogen peroxide (H₂O₂) as relatively stable reactive oxygen species gains considerable attention because it can regulate physiological and pathological processes. In order to better detect H₂O₂, fluorescent probes were widely applied. Over the past 20 years, a great deal of boronate-based fluorescent molecular probes appeared due to relatively simple oxidation reaction. However, the reaction mechanisms that boronate derivatives were converted into fluorescent product by H₂O₂ are poorly studied. In this paper, taking coumarin-7-pinacolboronate (CBU) as an example, the oxidation mechanism of boronate-based probes by various reactive oxygen species was studied by theoretical calculations. The results found that (1) the chemical reaction mechanisms are nearly identical for the reactions of CBU with hydrogen peroxide, hypochlorous acid, peroxynitrite, and tyrosine hydroperoxide, respectively. (2) There is not radical intermediate during the reaction. (3) The different reactive oxygen species has a strong influence on rate limiting step and reaction rate.

The intrinsic resistance energy ΔG^≠_XH/X of H-donor XH in hydrogen atom transfer (HAT) reaction is usually used to evaluate the kinetic H-donating ability. In this article, a new method for determining ΔG^≠_XH/X of H-donor in HAT reaction was proposed by the definition of thermo-kinetic parameter ΔG^≠o (XH) = 1/2[ΔG^≠_XH/X + ΔG^o (XH)]. ΔG^≠o (XH) is the characteristic physical parameter of XH to describe the H-donating ability in a chemical reaction during a certain reaction time, ΔG^o (XH) is the bond dissociation free energy. The kinetic studies of HATs between 20 alcohols, ethers, alkanes and amines (XH) with cumyloxyl radical [PhC (CH₃)₂O^•, CumO^•] were researched, and ΔG^o (XH), ΔG^≠_XH/X, and ΔG^≠o (XH) were used to investigate the H-donating abilities of the studied substrates in thermodynamics, kinetics, and HAT reaction. The effect of structures of XH on these three parameters, the structure–activity relationship, such as the influence of electronic, steric, polar and stereoelectronic effects of substituents, heteroatoms insertion in cycloalkanes, and cis–trans configurational isomerism on the H-donating abilities were discussed in detail. This study not only provides a new method for determining ΔG^≠_XH/X but also systematically studies the factors affecting the H-donating ability, laying a foundation for the selection, design, and synthesis of more efficient antioxidants.

4′-N,N-dimethylamino-3-hydroxyflavone (DMA3HF) has antioxidant activity and excited state proton transfer (ESIPT) property. In this study, the influence of electronegativity on the ESIPT process has been studied by DFT/TD-DFT methods. Except DMA3HF, the substitutes of S and Se have been designed. The analysis of main bond parameters, infrared vibration spectra, and reduced density gradient function shows that the reduction of atomic electronegativity could promote the ESIPT process. Dihedral angle, frontier molecular orbitals and hole-electron analysis indicate that the twisted intramolecular charge transfer (TICT) process has been enhanced by the decreasing electronegativity. The results show that the decrease of atomic electronegativity is beneficial to TICT and ESIPT processess.

As the mechanisms of the hydride transfer reaction between 7,8-dihydro-9-methylcaffeine (CAFH) with N-methylacridinium (AcrH⁺ClO₄^-) and hydrogen atom transfer (HAT) reaction between 2,3-dihydrobenzo-imidazoles (BIH) with 2,2-diphenyl-1-picrylhydrazyl radical (DPPH^•) were researched to both be induced by electron transfer, the reaction mechanisms of 2,3-dihydrobenzo-thiazoles (BTH) with these two substrates were studied. The thermodynamic analysis platforms were used to judge the mechanisms, and the mechanisms of these two reactions were not the same with CAFH and BIH as the E_ox (BTH) value was more positive than CAFH and BIH. A new method for inferring the reaction mechanism was proposed using the kinetic equation ΔG^≠_XH/Y = ΔG^≠o (XH) + ΔG^≠o(Y) and thermo-kinetic parameter ΔG^≠o. The HAT reaction mechanisms between BTH with DPPH^• and ^tBu₃PhO^• were researched by ΔG^≠o_HD. As the ΔG^≠o (BTH) values in these two reactions were similar; hence, the rate determining steps of them were both HATs as the ΔG^≠o_HD(Y) values of DPPH^• and ^tBu₃PhO^• used for determining ΔG^≠o (BTH) were both in HAT reactions. The HAT reaction mechanisms between BIH with ^tBu₃PhO^• were also researched by thermodynamic analysis platform and kinetic isotope effect (KIE = 3.99), which confirmed that the rate determining step of BIH/^tBu₃PhO^• was indeed HAT. The H-donating ability of BIH and BTH was compared by ΔG^≠o_HD. From BIH to BTH, the substitution of N by S not only greatly reduces the thermodynamic electron donating and H-donating capacity of the compound but also increases the H-donating ability in kinetics and HAT reaction.

Complexes of three aromatic diols, catechol, naphthalene-1,8-diol, and fluorene-4,5-diol, with a series of hydrogen bond acceptors (HBAs) that have oxygen, nitrogen, and sulfur acceptor atoms, have been studied by density functional theory (DFT) at the B3LYP/6-311+G(d,p) level. Binding energies, geometries, infrared spectroscopic (IR) frequencies, nuclear magnetic resonance (NMR) shifts, and measures of the electron density distribution from the Quantum Theory of Atoms in Molecules (QTAIM) are evaluated and compared with data for the corresponding monohydroxy compounds (monols), phenol, naphth-1-ol, and fluorene-4-ol, in order to assess the importance of cooperativity between intramolecular and intermolecular hydrogen bonding. All measures for all complexes show positive cooperativity whereby both the intermolecular and intramolecular hydrogen bonds are strengthened upon complexation. Cooperativity is weak for catechol and strong for the other two diols and, for all diols, increases with the hydrogen bond basicity of the acceptor. Correlations of IR and NMR metrics against binding energies for a single HBA and all six monols and diols are excellent, but attempts to correlate the same metrics for all HBAs and a single donor are frustrated by differences in intermolecular hydrogen bonding, depending notably on the identity of the acceptor atom in the HBA. Atom–atom interaction energies, calculated by the Interacting Quantum Atoms approach, are used to discuss the covalency of both types of hydrogen bond.