Infrared spectra of cyclic ethers and their derivatives

Data for the characteristic bands of cyclic ethers are reviewed. The infrared spectra of a number of 2-mono- and 2, 5-di-substituted derivatives of tetrahydrofuran are investigated. Absorption bands at about 900 cm⁻¹ are related to pulsation vibrations, and those at about 1200 cm⁻¹ to antisymmetric skeletal vibrations, of the tetrahydrofuran ring. It is shown that to confirm the presence of a tetrahydrofuran ring in a molecule, it is necessary to take into account not only the band of valence antisymmetric vibrations of the group C-O-C (ν _C-O-C ^as 1075 cm⁻¹), but also bands due to ring pulsation vibrations (ring symmetric valence vibrations ν _sk ^s ∼ 900 cm¹).     

PMR spectroscopic study of the kinetics of H/D exchange in methyl groups in a series of heterocyclic azines

The rate of H/D exchange among methyl group protons in a series of substituted 3-hydroxypyridines, 5-hydroxypyrimidines, and their N-oxides has been shown to increase with increasing acidity of the medium. The most reactive form of these molecules is the cationic form at pH<2. The rate of H/D exchange of CH₃ group protons in 3-hydroxypyridine derivatives has also been found to be several orders of magnitude lower than the rates of exchange for methyl-substituted 5-hydroxypyrimidine and its N-oxide. Effective rate constants for methyl group proton exchange have been estimated. In the case of methyl-substituted 5-hydroxypyrimidine N-oxide derivatives it has been established that the rate of proton exchange is greater for an ortho-methyl group than for a methyl group in the para-position relative to the N-oxide site.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 93–96, January, 1991.     

Fluorine absorption spectra and some fluorides in condensed state

The absorption spectra of liquid F₂, NF₃, N₂F₄, CF₄, BF₃, NF₃, SF₆ have been obtained at diminished temperatures in the near ultra-violet region of the spectrum. It is shown that the absorption spectrum does not differ from the spectra in the gaseous phase, therefore the elementary absorption act is characterized by the cross section of photon absorption by an individual molecule. The absorption cross sections of the above mentioned molecules are represented in the liquid phase, which do not differ strongly from absorption cross sections of these molecules in the gaseous phase. The dependence of the absorption cross sections of liquid fluorine on its concentrations in solutions with N₂, Ar, NF₃, O₂ at - 196°C has been studied. The cross sections of photon absorption by the fluoride molecule in different liquid media with small fluorine concentrations have been obtained.     

Intramolecular hydrogen bond in substituted 3-hydroxypyridines

To explain the character of the intramolecular hydrogen bond in substituted 3-hydroxypyridines, the chemical shifts in the NMR spectra of the hydroxyl group and the IR spectra were studied. It was established that the stability of the intramolecular hydrogen bond of the O-HNR₂ type in substituted 3-hydroxypyridines increases when compared with the corresponding phenols, while an opposite pattern is observed for bonds of the O-H0₂ N type. An approximate evaluation of the energy of the intramolecular hydrogen bond in substituted 3-hydroxypyridines was achieved. When reacting with bases of the same strength, 3-hydroxypyridine forms more stable complexes than phenol.     

Form of the dihedral angle dependence of the spin-spin coupling constant JHNNH

Cyclic hydrazides (derivatives of phtalhydrazide,pyrozolidone-3, indazolone, cyclic hydrazide camphoric acid) are studied by the NMR¹H method. The size of the dihedral HNNH angle of several model compounds (pyrozolidone-3, cyclic hydrazide norcamphoric acid) are calculated by the MINDO/3 SSF MO LCAO method. It is shown that in the hydrazides with HNNH dihedral angle 0–70° the magnitude of the HNNH spin-spin interaction constant does not exceed 1 Hz. The form of its dependence on the dihedral angle is determined.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 3, pp. 363–366, 1989.     

Structure of Aqueous Gallium(III) Bromide Solutions Over a Temperature Range 80–333 K by Raman Spectroscopy, X-ray Absorption Fine Structure, and X-ray Diffraction

The structure and complex formation of concentrated aqueous gallium(III) bromide (GaBr₃) solutions have been investigated over a temperature range 80–333 K by Raman spectroscopy, X-ray absorption fine structure (XAFS), and X-ray diffraction. The Raman spectra obtained at various [Br^?]/[Ga³⁺] molar ratios and temperatures have shown that complex formation between Ga³⁺ and Br^? occurs as a predominant species, with [GaBr₄]^? at [Ga³⁺] as high as 1～2 M (M = mol?dm ^?3) and [Br^?]/[Ga³⁺] ratios > ～2, and that cooling of the solutions favors the formation of the aqua Ga³⁺. The intermediate species were not seen in the Raman spectra. The XAFS data have revealed that the aqua complex has a sixfold coordination as [Ga(H₂O)₆]³⁺ with a Ga³⁺–H₂O distance of (1.96 ± 0.02) Å, whereas the [GaBr₄]^? complex has a Ga³⁺–Br^? distance of (2.33± 0.02) Å, and that vitrification of the aqueous GaBr₃ solution at liquid nitrogen temperature shifts the equilibrium toward the aqua complex. The X-ray diffraction data at different subzero temperatures have shown a tendency of decreasing Ga³⁺–Br^? and increasing Ga³⁺–H₂O interactions with lowering temperature, confirming the preference of aqua Ga³⁺ in the supercooled liquid state as well as in the glassy state. The Ga³⁺–H₂O distance of ～1.8 Å for the tetrahedral coordination was found in a 2.01 M gallium(III) bromide solution with a [Br^?]/[Ga³⁺] ratio of 3.7 and gradually increased to a value of 1.92 Å for octahedral geometry with decreasing temperature, suggesting that equilibrium shifts from [GaBr₄]^? to [Ga(H₂O)₆]³⁺ through intermediate species, [GaBr _n ]^(3?n)+ (n = 2 and 3). The Ga³⁺–Br^? and Br^?–Br^? distances within [GaBr₄]^? with an almost tetrahedral symmetry are (2.35± 0.02) and (3.82± 0.03) Å, respectively. The Ga³⁺ has the second hydration shell at (4.03± 0.03) Å and the hydration of Br^? is characterized with a Br^?–H₂O distance of (3.35± 0.02) Å at all temperatures investigated.     

Polynuclear nonfused bis(1,3,4-oxadiazole)-containing systems

Nonfused bis-1,3,4-oxadiazoles were synthesized by reaction of 5-substituted mono-and bis-tetrazoles with mono-and dicarboxylic acid chlorides. The results of kinetic studies showed that the transformation of tetrazoles into 1,3,4-oxadiazoles is accelerated by 1 to 2 orders of magnitude on addition of a catalytic amount of dimethylformamide, triethylamine, or pyridine.     

q-Weyl coefficients forU q (3) andq-Racah coefficients forSU q (2)

We show that theq-Weyl coefficients of the quantum algebraSU _q (3) are equal to theq-Racah coefficients of the quantum algebraSU _q (2) (up to a simple phase factor). Using aq-analog of the resummation procedure we obtain also theq-analogues of all known general analytical expressions for the 6j-symbols (or the Racah coefficients) of the quantum algebraSU _q (2) starting from one such formula.Presented at the 4th Colloquium Quantum groups and integrable systems, Prague, 22–24 June 1995.The research described in this publication was supported in part by Grants No. MB1000 and No. NRC000 from International Science Foundation.