Journal of Physical Organic Chemistry最新文献

In this study, synthesis, characterization, photophysical properties, and DFT calculations of a new tetraaryl-1,4-dihydropyrrolo[3,2-b]pyrrole (TAPP) derivative molecule of A-π-D-π-A type containing benzoxazole as an acceptor group at 1,4-positions have been carried out. The target A-D-A type molecule was synthesized using 4-(benzo[d]oxazol-2-yl)aniline by the method known in the literature, and it was aimed to obtain the classical TAPP structure in an iron-catalyzed environment. No product was obtained with the first method; therefore, the reaction conditions were optimized. The reaction time and temperature were varied in a controlled manner; the optimum conditions were determined with a reaction time of 7 h at 60°C. The photophysical behavior of the synthesized benzoxazole-substituted TAPP derivative was investigated by UV–vis and fluorescence spectroscopy depending on different solvent polarities. In the absorption spectra, the maximum absorption band observed around 330 nm in low polarity solvents shifted to 340 nm in polar solvents. Similarly, fluorescence emissions systematically red-shifted from hexane to DCM (470–550 nm), and quantum yields decreased significantly (0.41 in hexane and 0.03 in DCM). This bathochromic shift and decrease in intensity indicate that the molecule has high polarity in the excited state whereas the intrinsic charge transfer (ICT) and twisted ICT (TICT) states stabilize with increasing solvent polarity. At the same time, nonluminescent transition channels such as loss of planarity, oxygen-induced quenching, and internal conversion in the solvent-excited state also decrease the fluorescence intensity. The findings reveal that this TAPP derivative forms a strong donor-acceptor system and exhibits high sensitivity to solvent environment.

The structure of active centers of the KOH/NMP and KOBu^t/NMP superbase systems was studied using quantum chemical modeling with the combined B2PLYP-D2/6-311+G**//B3LYP/6-31+G* approach. It was shown that the closest solvation shell of the cation in both KOH and KOBu^t includes five N-methylpyrrolidone molecules. The structure of KOH·5NMP and KOBu^t·5NMP pentasolvate complexes was obtained and described. These complexes were then compared with similar dimethyl sulfoxide-based pentasolvate complexes previously studied, namely, KOH·5DMSO and KOBu^t·5DMSO. The effect of a water molecule on the structural and energy characteristics of superbase complexes with N-methylpyrrolidone was evaluated.

A series of biologically active phenothiazine derivatives were studied as inhibitors of the free-radical chain oxidation of isopropyl alcohol by atmospheric oxygen. It was found that these compounds exhibit antioxidant properties, effectively suppressing the oxidation process. The key rate constants quantitatively characterizing the efficiency of their antioxidant action were determined. Mathematical modeling was used to analyze the proposed oxidation mechanism, identifying the critical stages that determine the inhibitory efficacy of phenothiazines. It was shown that the inhibitor regeneration reaction plays a significant role, leading to a high inhibition capacity. The application of mathematical modeling allowed the proposal of an oxidation mechanism that provides a comprehensive explanation for all currently available experimental and literature data.

The intermolecular interactions between aniline (PhNH₂) and ethyl acetate (EtOAc) were investigated by using Raman spectroscopy and density functional theory (DFT) calculations. Experimental Raman spectra revealed red and blue shifts in the vibrational bands of PhNH₂, indicating the presence of weak hydrogen bonding and van der Waals interactions with EtOAc. A prominent hydrogen bonding was observed between the NH₂ group of PhNH₂ and the carbonyl (C=O) group of EtOAc. DFT calculations were performed to support the experimental findings, showing strong agreement. Molecular electrostatic potential (MEP) maps highlighted the electrophilic nature of the NH₂ group and the nucleophilic character of the C=O group, corroborating the observed hydrogen bonding. Frontier molecular orbital (FMO) analysis revealed that the HOMO–LUMO energy gap of PhNH₂···(EtOAc)_n (n = 1–3) complexes decreases with increasing number of EtOAc molecules, reaching a minimum of 4.69 eV. Quantum theory of atoms in molecules (QTAIM) analysis confirmed that the complexation is primarily governed by weak hydrogen bonding and van der Waals interactions involving N-H···O=C, H-N···H–C, and C-H···O=C contacts. This study provides valuable insights into solvent effects on the molecular behavior of aniline, with implications for both fundamental research and practical applications in physics and chemistry.

The relative stabilities of unsubstituted bicyclic bridgehead radicals have been previously shown to be dependent primarily upon differences in strain energies between the radicals and the corresponding saturated compounds. Although substituents are known to strongly affect the stability of acyclic carbon-based radicals, the effect of replacing at least one of the one-carbon bridges of bicyclic bridgehead radicals with a substituent was unknown. Because of geometrical constraints imposed by the bicyclic frameworks, the bridging substituents are unable to adopt conformations that optimize their stabilizing effects. Using [2.2.1] substituted derivatives as models, we have shown that substituents exert their effects via two primary modes. First, the presence of substituents influences the extent of hyperconjugative interactions between the SOMO and properly aligned bonds as revealed by NBO calculations. Second, when the substituents are frozen into a geometry reflective of that in the bicyclic radicals, they exert a direct impact upon the radical site that can be very different from that in the corresponding acyclic compounds. Neither of these effects alone rationalizes the relative stabilities of the radicals with various substituents. However, when combined, they offer a reasonable correlation with the observed relative energies. Generally, the effect of substituents on other bicyclic frameworks appears to follow a regular pattern of stabilization versus destabilization. The effect of changing the size of the bicyclic framework while maintaining the same substituent was also investigated. Generally, the order of relative energies mirrored that of the unsubstituted all-carbon analogs, suggesting that strain remains the primary factor in determining stability.