Journal of Physical Organic Chemistry最新文献

In this investigation, we have been compared and contrasted the substituent effects on stability using ΔΕ_s-t (E_t − E_s), frequency, ΔΕ_HOMO-LUMO (E_LUMO − E_HOMO), polarity, polarizability, Mülliken charge distribution and reactivity descriptors of the singlet and triplet Hammick silylenes derived from silapyridine-4-ylidene (1-s, 2x-s, 3x-s and 1-t, 2x-t, 3x-t; x = NH, PH, AsH, O, S, and Se) as well as the synthesized dialkylsilylenes by West (4-s), Denk (5-s), and Kira (6-s). In all cases, singlet (s) silylenes appear as ground states, exhibiting more stability than their corresponding triplet (t) states. All the above s and t silylenes appear as minima on their energy surfaces showing the positive force constant and the positive harmonic vibration frequency. Regardless of how orchestrated substituent groups in either “W” or “chair” position; the most stability is demonstrated by substitution of NH, and O groups in the fused pyrrole ring, while the least stability is considered by Kira's silylene. In contrast to previous report on the N-Heterocyclic Hammick carbenes, silylenes, and germylenes (NHCs, NHSis, and NHGes) that size, type, orientation, and the number of fused rings pronounced effect on stability of the corresponding divalent species, here σ-donor/π-donor groups (such as PH, AsH, S, and Se) similar to σ-acceptor/π-donor groups (such as NH and O) stabilize their corresponding silylenes. Furthermore, the scrutinized singlet silylenes reveal lesser nucleophilicity (N), greater electrophilicity (ω), higher chemical potential (μ), higher global hardness (η), and lower global softness (S) than the analogous triplet silylenes. All singlet and triplet species show the maximum electronic charge (ΔN_max) with positive sign.

Methyl pyropheophorbides-a possessing an o/m-(methoxycarbonyl)phenyl group at the 3-position were prepared by Diels–Alder reaction of 3-(trans-1,3-butadienyl)chlorin with methyl propiolate and successive didehydrogenation of the resulting 1,4-cyclohexadienes. The 3-arylated chlorin bearing the sterically demanding o-COOMe group as the major product was a 1:1 mixture of high-performance liquid chromatography-separable rotational isomers around the C3–C3¹ bond, while the minor product with the m-COOMe was less sterically hindered to exhibit rapid atropisomerization at room temperature. The 3-aryl group of the major product was nearly perpendicular to the chlorin π-system and less conjugated with the chlorin moiety than that of the minor product wherein more π-conjugation occurred to give slightly red-shifted Qy bands. Although both the atropisomers of the o-substitute in dichloromethane showed similar visible absorption bands and fluorescence emission data, their circular dichroism bands in the ultraviolet-C light region were dependent on the stereochemistry.

Despite the evidence on the antioxidant capability of estrogens, little is known about their reaction mechanism involved. According to the above, this work was carried out on the hydroperoxyl radical scavenging activity of three estrogens—estriol (EST), estradiol (ESD), and estrone (ESO)—in lipid and aqueous media by theoretical methodologies employing the DFT. In lipid and aqueous media, hydrogen transfer was the main reaction mechanism on the hydroperoxyl radical scavenging of EST, ESD, and ESO. The reaction rate constants calculated in lipid media were 1.08 × 10⁶, 8.39 × 10⁴, and 6.43 × 10⁴ M⁻¹ s⁻¹ for the EST, ESD, and ESO, respectively. The reaction rate constants calculated in aqueous media were 3.00 × 10⁶, 3.58 × 10^6, and 1.05 × 10⁸ M⁻¹ s⁻¹ on the hydroperoxyl radical scavenging activity of EST, ESD, and ESO, respectively. The results also showed that the EST, ESD, and ESO estrogens could scavenge high reactivity radicals through the SET mechanism in aqueous media. In lipid media, estrogens are moderate antioxidants, whereas in aqueous media, these are good antioxidants. These theoretical results support the intrinsic antioxidant activity of EST, ESD, and ESO estrogens in lipid and aqueous media.

The dinitrene 2,3,5,6-tetrafluoro-1,4-phenylenedinitrene was synthesized by photolysis of matrix-isolated 1,4-diazido-2,3,5,6-tetrafluorobenzene at 365 or 405 nm in high yields at cryogenic temperatures and characterized by FT-IR, UV-Vis, and EPR spectroscopy. The electronic structure of the dinitrene is described best as a quinoidal diradical with an open-shell singlet ground state and a triplet state laying only 650 ± 5 cal/mol higher in energy. Irradiation with λ = 254 nm results in fragmentation of the dinitrene into FCCF and several olefins which on prolonged photolysis fragment into FCCCN, FCCNC, and FCN.

The Diels–Alder reaction of three chiral dihydro-2H-[2,3-a]oxazolopyridines with N-methylmaleimide afforded the corresponding chiral cycloadducts as diastereomeric mixtures. In the presence of a solvent, some of the originally formed adducts underwent isomerisation to new isoquinuclidines.

Lead-free double perovskite materials A₂BI₆ (A = Cs, K, Rb; B = Pt and Sn) have been studied and analyzed invoking density functional theory (DFT). Computed values of the HOMO–LUMO gap for lead-free double perovskites material A₂BI₆ are found in the range of 1.062–2.811 eV. The energy gaps of K₂PtI₆, K₂SnI₆, and Rb₂SnI₆ are in the optimal energy gap range (0.9 to 1.6 eV) required for a lead-free double perovskite system. Conceptual DFT-based descriptors, viz., molecular hardness, softness, electronegativity, electrophilicity index, dipole moment, and polarizability, are computed. The result reveals that K₂PtI₆ shows high efficacy towards electron injection and may show the maximum electron driving force. The optical properties—refractive index and dielectric constant—of these perovskites are also computed. The maximum value of refractive index and dielectric constant is found for K₂PtI₆. Our computed results are in good agreement with the available experimental and other theoretical data. Perovskite materials K₂PtI₆, K₂SnI₆, and Rb₂SnI₆ display a suitable energy gap as well as a high refractive index and dielectric constant, which makes them suitable for photovoltaic applications.

1-Methyl-1,3,5-trisilacyclohexane was synthesized and its structure and conformational properties have been determined by gas-phase electron diffraction (GED) and quantum chemical (QC) calculations. The molecule may exist in two forms differing from each other by the substituent's position. QC results show that the equatorial conformer is predicted to be slightly more stable than the axial conformer; note that one method (M06-2X) with basis set 6-311G** shows an equal amount of Ax and Eq conformers: ratio (Ax/Eq) = (30–50):(70–50)% (depending on the method and basis set). From the GED data, the molar fractions of the conformers were found to be Ax:Eq = 54(10):46(10) at 280(5) K. A temperature-dependent Raman experiment resulted in an Ax:Eq ratio of 58(4):42(4). Conformational properties are compared in series of analogous 1-X-1-(hetero)cyclohexanes.

The reactivity of bis(2-chloroprop-2-enyl)sulfide in the system hydrazine hydrate/alkali has been studied using quantum-chemical methods. The B2PLYP-D2//B3LYP approach shows a good agreement between the relative values of activation barriers compared to high-precision CBS//Q-B3. The correction for the entropy change during the transition from the gas phase to the binary solvent hydrazine hydrate is calculated. The IEF PCM model was parameterized for hydrazine hydrate solvent. The studied reaction routes includes (i) a competition between migration of the C=C bond and dehydrochlorination of bis(2-chloroprop-2-enyl)sulfide; (ii) 1,3-prototropic rearrangements of bis (allenyl)sulfide resulting from a dehydrochlorination; (iii) the possible substitution of sulfur and chlorine atoms with hydrazine. The probable formation of the thiiranium and thiirenium cations formation in the above has also been evaluated.