Journal of Physical Organic Chemistry最新文献

Five triphenylamine-based dyes were theoretically investigated using density functional theory (DFT) and time-dependent density functional theory (TDDFT) due to their structural configuration of (D–π–A) which has potential applications as sensitizers for dye-sensitized solar cells (DSSCs). One dye was sourced from the literature, (E)-2-cyano-3-(5-(6-(diphenylamino)-3,3-dimethyl-3H-indol-2-yl)thiophen-2-yl)acrylic acid, denoted as (I), and the remaining dyes (from II to V) are inspired by the former with minor structural change in the indole moiety of donor part. These molecular structures are composed of different diphenyl indole amine species (donor part), thiophene (π-bridge), and cyanoacrylic acid (acceptor part). This study focused on the effect of small structural change in the five-membered ring of the indole moiety on the geometric, electronic, and optical properties of the studied dyes as well as their potential applications as sensitizers for DSSCs. Due to this structural change, a twist in the molecular skeleton of the designed dyes was observed, resulting in a new band at a longer wavelength that spans the visible region. This band is attributed to the phenomenon of twisting intramolecular charge transfer (TICT). The findings reveal that the minor structural change in the indole moiety enhanced the harvesting character of designed dyes that makes them promising candidates for application in DSSCs.

Halogen bond donors are recognized as electrophilic catalysts in reactions involving carbonyl compounds. This study describes an unexpected inhibition of the Knoevenagel condensation by the catalyst. To elucidate the intricacies of the inhibition mechanism, the overall reaction order and rate constants were determined using ¹H NMR spectroscopy, and further experiments with different nucleophiles were conducted. The findings revealed that the inhibition of the primary reaction is attributed to a substantial acceleration of the side reaction involving aldehyde methanolysis, which hinders the formation of the final alkene product.

This study theoretically investigates the factors controlling the periselectivity, chemoselectivity, and regioselectivity of the [3 + 2] cycloaddition reaction of aza-oxyallyl cation with cinnamaldehyde to form oxazolidinone. The research utilizes hybrid density functional theory (DFT) method at the B3LYP-D3, B3LYP, M06, and M062X coupled with the 6-311G (d, p) level of theories to explain that the [3 + 2] chemoselective addition of aza-oxyallyl cation across the carbonyl bond of cinnamaldehyde through its C and N reactive sites is more favorable than any other plausible mechanism. Generally, electron-donating groups (EDGs) on aza-oxyallyl cation decrease the activation barriers, whereas electron-withdrawing groups (EWGs) increase the activation barrier. The GEDT values predict a very low polar reaction for the [3 + 2] cycloaddition reaction.

The problem of environmental pollution by plastic is becoming more and more obvious. In this study, the non-catalytic reaction of diphenyl carbonate with methylamine as a model reaction for the depolymerization of polycarbonate was studied at the B3LYP/6-31++G(d,p) and M062X/6-31++G(d,p) levels. The reaction can proceed by the nucleophilic substitution and by the “addition–elimination” pathways. Calculations at the B3LYP/6-31++G(d,p) level indicate that the reaction of diphenyl carbonate with methylamine monomer leading to the formation of N-methyl-O-phenylcarbamate via the nucleophilic substitution pathway at 298 K is characterized by activation and reaction free energies equal to 174.0 and −57.1 kJ·mol⁻¹. The same reaction with methylamine dimer is characterized by activation and reaction free energies equal to 147.1 and −77.7 kJ·mol⁻¹, respectively. Thermodynamic and kinetic preference is also observed in the reaction of N-methyl-O-phenylcarbamate with the monomer and dimer of methylamine. Reactions with the formation of tetrahedral intermediates are unlikely. Their formation is endothermic and occurs with a decrease in entropy. This leads to small values of equilibrium constants. The equilibrium constant of the reaction of diphenyl carbonate with methylamine monomer to form a tetrahedral intermediate is 1.64·10⁻¹⁶ at 298 K and 1.20·10⁻¹⁴ at 423 K. The same trends are observed in the reactions of N-methyl-O-phenylcarbamate. The reactions of diphenyl carbonate, N-methyl-O-phenylcarbamate with methylamine dimer via the “addition–elimination” pathway are also characterized by small values of equilibrium constants. In all cases, interactions involving the methylamine dimer are more favorable than reactions involving the methylamine monomer.

Recent study on the effects of enzyme mutations on the primary kinetic isotope effects (1° KIEs) of H-tunneling reactions revealed that a more rigid system results in a weaker temperature dependence of KIEs, indicated by a smaller isotopic activation energy difference (∆E_a = E_aD − E_aH). In literature, a more rigid system has been defined by the presence of shorter, more densely populated hydrogen donor-acceptor distances (DADs) in both the productive reactant complexes (PRCs) and the tunneling-ready states (TRSs). Studying the relationship between DAD_PRC/DAD_TRS and ∆E_a can help validate existing H-tunneling models or guide the development of new theories. In a previous publication, we employed Hammett correlations on hydride acceptors (NAD⁺ analogues) to propose TRS electronic structures for qualitative analysis of DAD_TRS order. In this paper, we selected a pair of such systems and used secondary (2°) KIEs on the hydride donor (NADH analogue) to obtain quantitative DAD_TRS information at the molecular level. TRS structures were computed, and the corresponding 2° KIEs were calculated and fitted to the observed values to extract DAD_TRS data. PRC structures were also computed. The DAD_PRC/DAD_TRS information aligns with the rigidity order derived from Hammett correlation analysis, and the correlation between DAD_PRC/DAD_TRS and ∆E_a is consistent with observations in enzyme systems.

This study leverages machine learning to predict the activation energies of strain-promoted azide-alkyne cycloaddition (SPAAC) reactions. Using DFT calculations, 631 sets of bond angles and Mulliken charges from two acyclic alkynes were collected. Multiple machine learning models were trained on these data, achieving high accuracy (R² > 0.95). Both bond angle and charge were crucial for reliable predictions. The models successfully predicted activation energies for SPAAC reactions with unseen cycloalkynes, within certain limitations.

Inspired by distinguished characteristics of novel optical materials, there has been significant research interest in organic molecules that present excited-state intramolecular proton transfer (ESIPT) properties. Given the vital effects of substituent effect on molecular designs, in this study, we focus on probing into excited state behaviors of NHBQ-NO₂ (i.e., submitted by strong electron-withdrawing group -NO₂) and NHBQ-NH₂ (i.e., submitted by strong electron-donating group -NH₂). Exploring hydrogen bonding effects via photoexcitation, we verify the impact of substituent effect (-NO₂ and -NH₂) on interactions involving photo-induced hydrogen bonding effects, redistribution of charges, and associated phenomena related to ESIPT reaction. By comparing and quantifying the barriers for reactions in relative excited state, our results indicate electron-donating substituent -NH₂ enhances the ESIPT reaction for NHBQ fluorophore.

In this article, the proton transfer dynamics along a stable norharmane•(H₂O)_n (n = 2–4) hydrogen-bonded cluster on conversion from the neutral to cationic form of norharmane (NHM) in water medium was demonstrated experimentally and theoretically. The distinct absorption and emission bands of different prototropic forms of NHM are well-known in the literature. Initially, the conversion from neutral to cationic form of NHM on moving from a polar aprotic (acetonitrile) to a polar protic (water) solvent was ensured by steady-state absorption and fluorescence studies. The analysis of IR spectra and steady-state anisotropy data of NHM confirmed the possibility of the formation of a hydrogen-bonded network in the presence of water. The length of the network was explored and assumed by extensive Density Functional Theory (DFT) calculations. Then, by time-dependent density functional theory (TD-DFT), the excited state proton transfer (ESPT) pathway was established interrogating the NHM-water cluster with different numbers of water molecules. The theoretical analysis assured that the NHM•(H₂O)₂ cluster was incapable of maintaining the stable hydrogen bonding wire in the course of the ESPT mechanism. Rather, NHM•(H₂O)₃ and NHM•(H₂O)₄ clusters were simultaneously involved in operating the ESPT mechanism. The NHM•(H₂O)₄ cluster was more feasible to carry out the proton transfer than the NHM•(H₂O)₃ cluster. To the best of our knowledge, this was possibly the first theoretical evidence behind the conversion from neutral to cationic form of NHM via the formation of a hydrogen-bonded network.