Journal of Physical Organic Chemistry最新文献

The nonlinear optical (NLO) insights of triarylpyrazoline-based (Z)-2-(2-((7-(4-(5-[2,4-dimethylphenyl]-1-phenyl-4,5-dihydro-1H-pyrazol-3-yl)phenyl)-4,4,9,9-tetramethyl-4,4a,9,10a-tetrahydro-s-indaceno[1,2-b:5,6-b′]dithiophen-2-yl)methylene)-3-oxo-2,3-dihydro-1H-inden-1-yl)malononitrile (PR) and its derivatives P1–P7 were explored in this study. The compounds: PR and P1–P7 having donor–π–acceptor configurations and M06/6-311G(d,p) functional was selected to inquire the dipole moment (μ), linear polarizability (α), first hyperpolarizability (β), and second hyperpolarizability (γ). The findings of perturbed Kohn–Sham relations were deciphered to derive charge density of the molecules. The optical analysis was performed in gaseous phase and their findings were observed in 544.2–697.1 nm range. Moreover, the natural bond orbitals, frontier molecular orbitals, density of state, and transition density matrices for the aforesaid compounds were also calculated at aforesaid level. Global reactivity parameters of PR and P1–P7 were analyzed by using highest occupied molecular orbital–lowest unoccupied molecular orbital energies. Overall, all above-mentioned findings revealed significant optical nonlinear response in these pyrazoline-based scaffold (PR and P1–P7). However, among all the compounds, P3 has shown the highest nonlinearity with maximum μ_tot, <α>, β_tot, and γ_tot values at 19.4 D, 1.78 × 10⁻²², 2.57 × 10⁻²⁷, and 3.13 × 10⁻³² a.u., respectively. Hence, the current computational study might prove to be fruitful for the exploration of proficient NLO materials for optoelectronic devices.

Fullerene exhibits a wealth of interesting characteristics owing to its unique π-electron configuration. The structure and properties of fullerene can be manipulated by introducing chemical groups to the carbon–carbon bonds via organic reactions, extending its application field. The Diels–Alder (DA) cycloaddition reaction is commonly used to decorate the carbon cage of fullerene. Furthermore, atoms, ions, clusters, and molecules can be inserted into the hollow carbon cage of a fullerene, thereby changing the electron transfer process within the fullerene cage and thus the reactivity of the as well as the regioselectivity of the DA cycloaddition reaction. Computer-based theoretical modeling is an essential tool for studying chemistry. Herein, we provide a brief review of theoretical investigations into the cycloaddition mechanism of two most common fullerenes (C₆₀ and C₇₀), especially in terms of the effects of encapsulated chemical species based on the distortion–interaction model. We hope that the current mini review will provide a useful and interesting resource for researchers working on—or simply being interested in—the in silico investigation of fullerenes and their DA-based modification.

The irradiation of water solution of cytidine with UVC light showed that the compound participates in a tautomerism following the kinetics of a first-order reaction. The PIDA mechanism showed that the proton detachments in the tautomers of cytidine occur through the repulsive ¹πσ* excited states and lead to conical intersections S₀/S₁, whose structures were optimized. More probable is the IRC mechanism, which proceeds along ¹nπ* excited state reaction paths. This mechanism includes a water molecule as a catalyst, which assists the phototransformation of amino-oxo tautomer of cytidine into imino-hydroxy one.

Using density functional theory, polyols were used as model ligands for Cu⁺/Cu²⁺ complexes to study the role of the hydrogen bond network on the metal binding affinity. In addition to the gas phase studies, the calculations were performed in 1-decanol and DMSO solvents. The Cu²⁺ complexes were the most stable complexes with the highest bond dissociation energies (BDE). The presence of three H-bonds in the first shell increased BDE values up to 17.99 and 57.07 kcal/mol for Cu⁺ and Cu²⁺ complexes in the gas phase, respectively, whereas the presence of another three H-bonds in the second shell increased BDE values up to 7.27 and 24.35 kcal/mol for Cu⁺ and Cu²⁺ complexes in the gas phase, respectively. Therefore, this H-bond network caused, for example, a more stable Cu⁺ complex with a formation constant of 1.4 × 10¹⁷ times. The natural bond orbital (NBO), atoms in molecules (AIM), and reduced density gradient (RDG) analyses showed that the intramolecular hydrogen bond network led to the enhancement of metal-binding affinity.

Cyclopentane-1,3-diyl diradicals (DRs) provide excellent opportunities to study the properties of diradicals because their lifetimes can be significantly lengthened to up to milliseconds with the introduction of proper substituents. This study investigated the bonding characteristics of singlet and triplet DRs having C=O and p-cyanophenyl groups (S-DR3 and T-DR3) by monitoring the photo-induced formation of the diradicals from their precursor azo compounds using time-resolved IR (TR-IR) spectroscopy. Upon the formation of S-DR3, a C=O stretching wavenumber was upshifted by 22 cm⁻¹, whereas a C≡N stretching one was downshifted by 12 cm⁻¹. The observed shifts indicate that the unpaired electrons increase and decrease the C=O and C≡N bond orders, respectively. The effects of the unpaired electrons in S-DR3 were similar to those observed in our previous TR-IR studies on a singlet cyclopentane-1,3-diyl diradical having C=O but no C≡N groups (S-DR2) and on that having C≡N but no C=O groups (S-DR1), respectively. Contrastingly, upon the formation of T-DR3, the C=O wavenumber was downshifted by 16 cm⁻¹, indicating that the unpaired electrons decrease the C=O bond order. More notably, no detectable shifts were observed in the C≡N stretching wavenumber. These observations are not clearly explained by a model suggested in the previous studies on S-DRs. Here, we discuss and propose a more elaborated resonance hybrid of DRs that can explain the directions and relative magnitudes of the observed wavenumber shifts irrespective of spin multiplicities. We expect that the findings and suggestions presented here will stimulate research in both organic and theoretical chemistry.

This contribution reports influences of unusual conformational metamorphosis shown by Reichardt's and Brooker's metameric zwitterions by an earlier work, on various intrinsic electronic and optoelectronic properties. Detailed quantum mechanical investigations were carried out using HF, B3LYP, CAM-B3LYP, and ωB97xD methodologies. Observations suggest that whereas certain properties were directly and strongly influenced by the conformation preferences (twisted vs. planar), others were not strongly inclined to such conformational transformations. Interestingly, even with inherent conformational differences, observed properties were found to have only one major contributing component in each molecule and can be beneficial in one dimensional (1D) or pseudo-1D chromophore design strategies. Both coupled perturbed (CP) and finite field (FF) theories were used to compute dipole moments, polarizabilities, and hyperpolarizabilities, and so on, and excellent agreements (or exact matching results) were observed between the two theories. Reichardt's metamer was found to be more efficient in many aspects than Brooker's metamer. The direct and strong influences of metameric manipulations on structure–property correlations shown in this work can be adopted as a useful strategy for efficient chromophore design. Such a strategy is useful in the field of nonlinear optics, and may also find applications in various other areas of material sciences.

The tandem reactions of 2,5-bis(trifluoromethyl)-1,3,4-oxadiazole with conjugated, unconjugated, acyclic, and cyclic dienes have been studied at the M06-2X/6-311++G(d,p) level of theory. The rate-determining step is the initial [4+2] cycloaddition in the tandem reaction of 2,5-bis(trifluoromethyl)-1,3,4-oxadiazole with acyclic, cyclic, conjugated, and unconjugated dienes, whereas the stereochemistry of the tandem adduct is determined by the [3+2] step. The exo-coupling is kinetically favored over the endo-coupling in the initial [4+2] reaction of 2,5-(bis-trifluoromethyl)-1,3,4-oxadiazole with all the considered dienes. In the retro [3+2] step (N₂ extrusion), higher activation energy is required to furnish the carbonyl ylide in the reaction of 2,5-(bis-trifluoromethyl)-1,3,4-oxadiazole with conjugated and unconjugated cyclic dienes as compared with the reaction with unconjugated acyclic dienes. At the stereochemistry [3+2] step, the intermolecular addition is kinetically favored over the intramolecular addition in the [3+2] reaction of 2,5-(bis-trifluoromethyl)-1,3,4-oxadiazole with both conjugated or unconjugated cyclic dienes and unconjugated acyclic dienes. The reaction proceeds with low activation energies when conjugated and unconjugated cyclic dienes are participating, compared with those of unconjugated acyclic dienes. Overall, the tandem process proceeds via an asynchronous one-step mechanism [4+2] coupling in an exo- or endo-cycloaddition fashion, followed by a retro [3+2], which extrudes the N₂, and then the stereo-determining intermolecular or intramolecular [3+2] cycloaddition step, which leads to the tandem products. The polarity of both inter- and intra-molecular cycloaddition steps can be influenced by two factors: the nature of the heteroatom present on the diene molecule and the size of the cyclic diene. These factors play a role in determining the reactivity and electron distribution within the diene, thereby impacting the overall polarity of the cycloaddition reactions.

The influence of ethylene substitution and the tether length between the two reacting counterparts on the selectivity and reactivity of the intramolecular [3 + 2] cycloaddition (IM32CA) reactions of cyclic nitrones leading to tricyclic isoxazolidines have been studied within the Molecular Electron Density theory at the MPWB1K/6-311G(d,p) computational level. These zw-type IM32CA reactions follow one-step mechanism, and the activation barrier decreases with the introduction of electron withdrawing (EW) substituent at the alkene moiety in both the intramolecular and intermolecular versions. The IM32CA reactions involving unsubstituted alkene have non-polar character with minimal electron density flux classified as null electron density flux type, while that involving the EW nitro substituted ethylene is more facile with a strong electron density flux from the nitrone to the ethylene moiety, classified as forward electron density flux type. The increase in the polar character of the IM32CA reaction decreases the activation Gibbs free energies associated with these intramolecular processes, while the highly polar IM32CA reactions are disfavored with respect to the intermolecular ones. Interestingly, the preferred regioselectivity observed in low polar IM32CA reactions having three methylene units between the nitrone and ethylene frameworks is reversed to that in nitrones separated with four methylene units, in conformity with the experimental outcome. Finally, electron localization function and quantum theory of atoms-in-molecules studies reveal that, in general, these IM32CA reactions involve early transition state structures in which the formation of new C-C and C-O single bonds have not yet started.

A fruitful debate took place recently in literature, discussing the enhanced Diels–Alder reactivity of tropone derivatives for which the carbonyl polarity was reversed by means of umpolung. Karas et al. sustained that the umpolung increases the antiaromatic character of the ring, affecting the highest occupied molecular orbital (HOMO)/least unoccupied molecular orbital (LUMO) energies, speeding up the reaction. Tiekink et al. challenged this interpretation by sustaining that the asynchronicity of the reaction mechanisms, rather than orbital energy perturbation, was the main responsible for the smaller reaction barriers. We shed light on this dispute by computing full interaction quantum atom (IQA) and quantum theory of atoms in molecules (QTAIM) analyses over complete intrinsic reaction coordinate (IRC) paths for the Diels–Alder reaction of tropone and its umpolung derivatives, using the same systems studied by Karas et al. and Tiekink et al. Our results confirm that the asynchronicity is indeed very high for those reactions with smaller reaction barriers and offer an atom-by-atom and bond-by-bond analysis of the entire IRC pathways. Even though asynchronicity and lower reactions barriers seem to be related, antiaromaticity and lower barriers are related as well, but discussing both these interpretations does not necessarily require arguments on HOMO/LUMO energies to be invoked.

The asymmetric oxirane ring-opening reaction leading to the formation of regioisomeric chlorohydrin esters was studied in the reaction series “acetic acid–epichlorohydrin–tetrahydrofuran (nitrobenzene)–trialkylamine” by kinetic methods and FT-IR spectroscopy. The effect of solvent polarity and the structure of tertiary amines on the regioselectivity and reaction rate were studied. Tertiary amines with comparable basicity but different nucleophilicity and spatial structure were chosen as catalysts. It was shown that in solvents of different polarity, the components of the initial reaction system are present both as hydrogen-bonded complexes and as individual substances. The reaction orders with respect to acid and amine in solvents of different polarity were established. Correlations between the reaction rate and the parameters of nucleophilicity and structure of amines as well as the polarity of the solvent were established. The regioselectivity of the reaction was studied by ¹H NMR spectroscopy using the ratio of regioisomeric reaction products. It was shown that the regioselectivity and rate of catalytic acetolysis of epichlorohydrin are effectively controlled by the structure of tertiary amines and the polarity of the solvent. The scheme of reaction regio-flows was detailed.