Results 1 - 10 of 25062
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[en] The data on the methods of synthesis and chemical properties of 3-cyanopyridine-2(1H)-chalcogenones published over the last 20 years are systematised and analysed. Special attention is given to the use of these compounds as building blocks in the synthesis of fused O,N,S-heterocycles.
[en] The published data on nitro derivatives of 1,3,5-triazine, belonging to the class of high-energy substances, have been systematised for the first time. The properties of C-nitrotriazines, nitraminotriazines and nitroalkyltriazines are considered. The data on the synthesis of previously unknown trisubstituted 1,3,5-triazines containing various functional groups including trinitromethyl groups are generalised.
[en] Information on the methods of synthesis of 4-aryl- or 4-hetaryl-substituted pyridines developed in the recent years is discussed and generalised. Examples of the practical use of 4-(het)arylpyridine derivatives are given.
[en] An investigation was carried out on the effect of hydrostatic pressure on hindered rotations and phase transition in s-triazine by methods of N14 pure nuclear quadrupole resonance (PNQR). Resonance frequencies and relaxation times were measured as a function of pressure up to 6 Kbar at various temperatures, with special attention paid to the transition region. A brief review of the quadrupole interaction of a spin I=1 nucleus is given and the response of a quadrupolar nuclei system to r.f. pulses is discussed. The molecular and crystallographic structure of s-triazine is described. The contribution of these rotations to the longitudinal and transversal relaxation times T1 and T2 is calculated. Methods for measuring T1 and T2 and the experimental results are discussed; these results are consistent with the calculations performed. Theories of the phase transitions and the experimental results near Psub(c) are discussed. The splitting of the nq 2 lines, Δν, above the transition is found to vanish on approaching Tsub(c) with a critical exponent β=1/2. This result is consistent with previous Δν vs. temperature measurements and are in accord with the Landau theory. (B.G.)
[en] Ab initio molecular orbital calculations at the SCF level have been utilized to determine the structure and the electronic and vibrational properties of 2,6-lutidine (2,6-dimethyl-pyridine) in the ground electronic state. Comparative calculations have been performed on the parent molecule pyridine. Structure predictions of both molecules are in good agreement with experimental data. The most stable rotamer of 2,6-lutidine has C2v symmetry with one of the C-H bonds of both the methyl groups lying in the plane of the aromatic ring and pointing in the opposite direction with respect to the nitrogen atom. This is the result of the minimization of competing forces deriving from steric hindrance and electronic stabilization. Vibrational frequencies and oscillator strengths of C-H stretching in the fundamental region have been calculated for both pyridine and the most stable rotamer of 2,6-lutidine and compared to IR data obtained in pure liquids. The potential energy profile of the C-H bond in and out of plane has been investigated up to five times the equilibrium distance. The trend of the potential curves confirms that the C-H bond lying in the plane has a higher dissociation energy than that of the in-plane bonds as observed in experiments on vibrational overtones
[en] Published data on the synthesis of quinoxalines are generalized and described systematically; the key attention is given to the sources published in the last 10-15 years. Modifications of the classical synthetic routes and new methods little known to wide circles of chemists are considered.
[en] The published data on the methods for the synthesis of furazans fused to six-membered heterocycles with two heteroatoms in positions 1 and 4, their reactivities and practical applications are considered and systematised.
[en] A series of novel branched derivatives of 6-aryl-2,4-diamino-1,3,5-triazine from corresponding aryl nitriles and dicyanodiamide was synthesized. These compounds show a nanodispersibility and good thermal stability.
[en] 2 alkyl, aryl and halogen derivatives of 6-fluoro-2-R-7-methyl-5-oxo-5-H-1,3,4-thiadiazole[3,2,-a] pyrimidine were prepared by reaction of 2-R-5-amino-1,3,4-thiadiazole and ethyl-2-fluoro-acetoacetic ester. (author)