Analysis of the Tautomeric Properties of 2-Formylcyclopentane-1,3-Dione Using the Data of IR Spectroscopy and Nonempirical (ab initio and DFT) Quantum-Chemical Calculations

The tautomerism, spectral properties, and properties of intramolecular hydrogen bonds in 2-formylcyclopentane-1,3-dione (FCPD) have been investigated by the methods of nonempirical quantum chemistry (calculations by the ab initio and DFT methods) and IR and ¹³C NMR spectroscopy. It is shown that FCPD in a crystalline form, as also does malonic dialdehyde, exists as self-associated enolized molecules with an open chelate ring. It is found that in solutions in CCl₄ the compound investigated exists as an equilibrium mixture of its exo- and endoenolic forms, with predominance of the former. The IR spectra of the solutions of FCPD in CCl₄ fix the presence of small amounts of the associate formed from the anionic and protonated forms of the substance. For the first time, the energies of the intramolecular H bonds of the endo- and exoenolic tautomeric forms in FCPD have been estimated theoretically. They appeared to be equal to 3.69 and 4.91 kcal·mole^–1, respectively. The possible mechanisms of enol-enolic interconversions of FCPD have been discussed.     

Scission of oxiranes by acid anhydrides to unsaturated alcohol esters

The reactions of some 1-R-3-methyl-2,3-epoxybutanes with acetic and propionic anhydrides takes place at 140–160C, regioselectively, with the formation of -metallyl alcohol esters.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 309–312, March, 1989.     

Long-lived room temperature phosphorescence of a naphthalene—β-cyclodextrin—adamantane complex in the presence of oxygen

Naphthalene-d₈—-cyclodextrin—adamantane triple complexes were prepared in an aqueous solution at room temperature. Irradiation ( = 285 nm) of the solution in the presence of molecular oxygen results in the long-lived ( = 10.3 s) room temperature phosphorescence (RTP). The removal of oxygen from the solution increases the RTP intensity and phosphorescence lifetime by 1.5 times. The RTP spectrum contains a well-resolved vibrational structure, whose bands are assigned to full symmetric vibrations of naphthalene, their overtones, and the combination tones of full symmetric vibrations. The quantum-chemical calculation of the triple complex structure confirms that both naphthalene and adamantane can simultaneously be included into the -cyclodextrin cavity and suggests that the role of the latter as the third component is the more efficient shielding of naphthalene from the oxygen effect due to both the formation of three-component complexes and their aggregation to form submicronic particles.     

Molecular photonics of polymethine dyes in complexes with cucurbit[7, 8]urils

Thiacarbo- and thiadicarbocyanine indolenine and thiazoline polymethine dyes form host?guest complexes with cucurbit[7,8]urils in water. Cucurbit[7]uril forms preferentially 1: 1 and 1: 2 monomeric complexes and cucurbit[8]uril forms 2: 1 and 2: 2 dimeric complexes. On the basis of quantum-chemical calculations, the structure of monomeric and dimeric complexes has been suggested. The complexation manifested itself in absorption, prompt and thermally activated delayed fluorescence spectra, as well as in the triplet?triplet absorption spectra. Dimeric complexes in the triplet state are involved in one-electron oxidation and participate in triplet?triplet energy transfer.     

Determination of the factorized atomic part of the X-ray absorption cross section in the near-edge spectrum: Application to the analysis of structural changes in β zeolite with an increase in the aluminum content

A technique for determining the factorized atomic part σ_at(k) of the X-ray absorption cross section in the near-edge range of small photoelectron wave numbers k, based on the selection of this function from the experimental absorption spectrum of the atom in a compound, has been developed. This technique has been tested using the X-ray absorption near-edge structure (XANES) spectra of aluminum and silicon in a number of model compounds with known structure and applied to investigation of changes in the character of the short-range environment of a silicon atom in β zeolite with a variable Si/Al ratio. Use of the function σ_at(k) obtained by the developed technique in the ab initio calculation of the XANES spectra of silicon in a model β zeolite with Si/Al = 100 makes it possible to reduce the effect of the errors of the muffin-tin approximation on the fine structure of the calculated spectrum and substantiate the possibility of comparing relative changes in a certain spectral range with a change in the structure of the short-range environment of silicon in β zeolite with an increase in the aluminum content. On the basis of this approach, the formation of local distortions in the oxygen tetrahedron coordinating an ionized silicon atom with an increase in the aluminum content (decrease in the Si/Al ratio from 100 to 12) has been established.     

Local Structure of Copper Centers Obtained during Solid-Phase Synthesis in Copper–Mordenite Zeolite

Technical Physics - The influence of temperature conditions for synthesis on the nearest-neighbor environment of copper atoms in copper–mordenite zeolites produced by solid-phase ion exchange...     

Synthesis of Amides by Nucleophilic Substitution of Hydrogen in 3-Nitropyridine

3-Nitropyridine reacted with nitrogen-centered carboxylic acid amide anions in anhydrous DMSO in the presence of K₃Fe(CN)₆ via oxidative nucleophilic substitution of hydrogen to give previously unknown N-(5-nitropyridin-2-yl) carboxamides. The reaction of nitrobenzene with urea anion in DMSO enabled one-pot synthesis of bis(4-nitrophenyl)amine.     

Spectral properties and structures of supramolecular complexes of naphthylpyridine with β-cyclodextrin

The electronic absorption and fluorescence spectra of 4-(2-naphthyl)pyridine (1) and N-methyl-4-(2-naphthyl)pyridinium perchlorate (2 ⁺·ClO₄ ^–) were studied in aqueous solutions in the absence and presence of -cyclodextrin (-CD). In aqueous solutions and organic solvents in the presence of water or H⁺ ions, compound 1 exhibits intense fluorescence with a maximum at 21 270 cm^–1, and its quantum yield in an aqueous solution is 0.9±0.09. The same fluorescence spectrum was detected for an aqueous solution of 2 ⁺·ClO₄ ^–. In an aqueous solution, compound 1 and -CD form stable fluorescing supramolecular 2:2 complexes, whose structure was calculated by the quantum-chemical MNDO/PM3 method. The formation of these complexes induces a hypsochromic shift of the fluorescence maximum of 1 by 5000 cm^–1. The stability constant of the complex is 2·10³ L mol^–1. A decrease in the pH results in the formation of a protonated form of 1(1·H⁺) and destruction of the complex, thus favoring the escape of the substrate from the -CD cavity. The quantum-chemical calculations showed that the insertion of 1 into the -CD cavity is thermodynamically more favorable than hydration; on the contrary, the formation of 1·H⁺ increases dramatically the hydration energy, which promotes the escape of 1·H⁺ from the -CD cavity; cation 2 ⁺ does not form a complex with -CD; in the thermodynamically most favorable 2:2 complex, the naphthalene fragments of two molecules 1 are parallel to each other in a broad section of the -CD dimer constructed according to the head-to-head type.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2420–2425, November, 2004.     

Crown-containing butadienyl dyes. 5. Structure and photoisomerization of a butadienyl dye containing a 15-crown-5 fragment

The structure of the E,E isomer of a butadienyl dye of the benzothiazole series containing a 15-crown-5 fragment was established by X-ray diffraction analysis. The stacking motif of the dye molecules in the crystal structure is, apparently, attributable to intermolecular -interactions between the large conjugated fragments. The possibility of [2+2] photocycloaddition occurring in the crystal is discussed. Reversible geometrical photoisomerization of the dye and its complex with Mg²⁺ in acetonitrile solution was studied by spectrophotometry and ¹H NMR spectroscopy. Photoirradiation of the complex of the E,E isomer with Mg²⁺ leads predominantly to isomerization of the C=C bond adjacent to the benzothiazole fragment. Regioselective E,EZ,E photoisomerization occurs via a singlet mechanism with a quantum yield of about 0.45. The quantum yield of reverse Z,EE,E photoisomerization is approximately 0.52. The structures of different geometrical isomers of the dye complex with Mg²⁺ were calculated by the quantum-chemical density functional theory (DFT).