Free radicals in vicarious C-amination reactions of 1-methyl-4-nitropyrazole

The primary radical anions of substrate in the reactions of vicarious nucleophilic substitution of hydrogen in 1-methyl-4-nitropyrazole with 1,1,1-trimethylhydrazinium iodide and 4-amino-1,2,4-triazole in t-BuOK-DMSO were observed and identified by EPR monitoring. The probable mechanism of the substrate radical anions formation is discussed.     

The silafulvene: a potentially stable compound containing a double carbonsilicon bond

Two conformations of dimethylsilafulvene are calculated via a CNDO/2 procedure. One of them is planar while in the other the CH₃SiCH₃ plane is perpendicular to the cyclopentadienyl ring plane. The conformation energies differ by 19.8 kcal/mol.     

Dichroism in transmission of light by an array of self-assembled GaAs quantum wires on a nanofaceted A(311) surface

Dichroism in the transmission of light (the dependence of the transmittance on the direction of polarization of light) is revealed in corrugated GaAs/AlAs superlattices grown on a nanofaceted A(311) surface. It is assumed that the observed effect is associated with the structural anisotropy, i.e., with the formation of an array of GaAs quantum wires. This inference is confirmed by high-resolution electron microscopy. The GaAs/AlAs superlattices containing quantum wires also exhibit polarization anisotropy of the photoluminescence observed in the yellow-red spectral range.     

Unexpected synthesis of a novel heterocyclic system – (7E,10aE)-2,7-Dimethylfuro[3′,4′:6,7]cycloocta[1,2,3-cd]indole-8,10(2H,6H)-dione

The first derivative of a novel heterocyclic system, (7E,10aE)-2,7-dimethylfuro[3′,4′:6,7]-cycloocta[1,2,3-cd]indole-8,10(2H,6H)-dione, was synthesized based on the Stobbe condensation of 3-chloro-1-methylindole-2-carbaldehyde with diethyl isopropylidenesuccinate. Cyclization of the 2-indolyl-containing diacid, formed by subsequent hydrolysis of the condensation product, did not lead to the expected fulgide, but rather to an unprecedented tetracyclic compound, the structure of which was established by ¹H, ¹³C NMR, IR spectroscopy, mass-spectrometry and single crystal X-ray diffraction.     

Isoenergetic Polymorphism: The Puzzle of Tolazamide as a Case Study

In the present case study of tolazamide we illustrate how many seemingly contradictory results that have been obtained from experimental observations and theoretical calculations can finally start forming a consistent picture: a “puzzle put together”. For many years, tolazamide was considered to have no polymorphs. This made this drug substance unique among the large family of sulfonylureas, which was known to be significantly more prone to polymorphism than many other organic compounds. The present work employs a broad and in‐depth analysis that includes the use of optical microscopy, single‐crystal and powder X‐ray diffraction, IR and Raman spectroscopies, DSC, semiempirical PIXEL calculations and DFT of three polymorphs of tolazamide. This case study shows how the polymorphs of a molecular crystal can be overlooked even if discovered serendipitously on one of numerous crystallizations, and how very different molecular packings can be practically isoenergetic but still crystallize quite selectively and transform one into another irreversibly upon heating.     

Structural studies of nanomaterials by the radial electron density distribution method with the use of synchrotron radiation in transmission mode

The efficiency of the application of the transmission X-ray diffraction technique implemented with the use of the VEPP-3 synchrotron radiation source to obtain functions of the radial electron density distribution (REDD) is shown. By the example of a poorly crystallized sample of cerium oxalate the possibilities of the obtained REDD functions in the structural diagnostics of X-ray amorphous materials are demonstrated: the oxalate phase is detected, the features of the local structure are revealed, and the size of the atomic ordering region is determined.