First example of the formation of bipolar spiro σ-complexes from 6-bromo-5,7-dinitrobenzo[e]-1,2,3,4-tetrazine 1,3-di-N-oxide

The reactions of 3,5,7-trimethyltropolone and 2-(N-benzylamino)tropone with 6-bromo-5,7-dinitrobenzo[e]-1,2,3,4-tetrazine 1,3-di-N-oxide afforded novel bipolar spiro -complexes. The kinetic and activation parameters of the R,S-enantiotopomerization of a chiral spiro -complex of 2-(N-benzylamino)tropone were determined using dynamic ¹H NMR spectroscopy.     

1,3-dioxenium cations: Synthesis and properties

The features and prospects of the new reaction of 1,3-keto-enols, ketones, and acids yielding 1,3-dioxenium salts were investigated. The results of studies of the structure, topomerization, and transformations of 1,3-dioxenium cations — a new family of stable heterocyclic cations of the allyl type — were generalized.     

Ethynyl carbonium ions. 1. Reaction of 2.6-diaryl-4-phenylethynylpyrulium perchlorates with oxygen-containing nucleophiles

When 2,6-diaryl-4-phenylethynylpyrylium perchlorates are refluxed in water, methanol, or ethanol, they are converted to monomethinecyanines, the formation of which is explained by hydration of the phenylethynyl group and subsequent [2+2]-cycloaddition of the resulting 2,6-diaryl-4-benzoylmethylenepyrans to the starting pyrylium salt. The corresponding pyridine derivatives were obtained by the action of ammonia and aniline on the monomethinecyanines. The IR and PMR spectra of the compounds and the results of x-ray diffraction analysis of 2,6-diphenyl-4-[1-(2,6-diphenyl-4-pyranylidene)-2-phenyl-3-benzoylallyl]pyridine are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 885–890, July, 1988.     

Synthesis, structures, and properties of spiro[6-azaperimidine-2,4′-cyclohexa-2′,5′-dien]-1′-one derivatives

The reaction of 5-amino-4-chloroquinolines with 4-amino-2,6-di-tert-butylphenol yielded derivatives of spiro[6-azaperimidine-2,4′-cyclohexa-2′,5′-dien]-1′-one, which exhibit photo-and thermochromic properties in solutions. The structure of 2′,6′-di-tert-butyl-5,7,9-trimethylspiro[6-aza,-2,3-dihydroperimidine-2,4′-cyclohexa-2′,5′-dien]-1′-one was established by X-ray diffraction study. The ring-chain isomerization of 2′,6′-di-tert-butyl-5,7-dimethyl-and 2′,6′-di-tert-butyl-5,7,8-trimethylspiro[6-aza-2,3-dihydroperimidine-2,4′-cyclohexa-2′,5′-dien]-1′-ones was studied by dynamic NMR spectroscopy. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2028–2034, November, 1997.     

Dielectric characteristics of the relaxor state of the perovskite ceramics 0.9(Na1 − x K x Bi)1/2TiO3-0.1Bi(ZnTi)1/2O3 near the morphotropic phase boundary

X-ray diffraction investigations have revealed that, in the system of solid solutions 0.9(Na_{1 ? x} K _x Bi)_1/2TiO₃-0.1Bi(ZnTi)_1/2O₃, there is a morphotropic phase boundary in the potassium concentration range of x ≈ 0.25, which separates the regions of compositions with rhombohedral (R3c) and tetragonal (P4mm) structures. It has been shown that, in the vicinity of this boundary, ceramic samples of the studied system exhibit properties of relaxor ferroelectrics. The results of the investigation into the dielectric properties of relaxor ceramics of the composition x = 0.3 with the use of the impedance spectra measured in the frequency range from 25 to 10⁶ Hz at temperatures from 100 to 900 K have been presented. It has been found that, in the temperature region of the existence of the relaxor state lying below the temperature corresponding to the maximum of the real part of the permittivity (T′ _m = 550 K), the dielectric polarization is determined by the sum of the contributions from the matrix and dipole clusters. The temperature dependence of the contribution from the clusters, which is determined by the kinetics of their formation and freezing, is characterized by a curve with the maximum at approximately 400 K. The process of freezing of dipole clusters occurs over an extended temperature range of more than 200 K.     

Dielectric properties of perovskite ceramics of (1–x)BiFeO3 ? x(KBi)1/2TiO3 (0.40 < x < 0.85) solid solutions from impedance spectroscopy data

The dielectric properties of the ceramics of (1 − x)BiFeO₃ − x(KBi)_1/2TiO₃ (0.40 < x < 0.85) solid solutions with an orthorhombic structure have been studied using impedance spectroscopy in the frequency range 25–10⁶ Hz at different temperatures. It has been shown that these solid solutions undergo a diffuse ferroelectric phase transition. The Curie temperature is found to be in the range 620–640 K. The activation energies of dielectric polarization relaxation (δE _M ) and dc charge carriers (ΔE _dc) are determined. It has been established that, in the vicinity of 460 K, ΔE _dc increases jumpwise as the temperature increases.