Two crystalline polymorphic forms of α-(<Emphasis Type="Italic">N</Emphasis>-benzoxazolin-2-one)acetic acid

Two crystalline polymorphic forms of α-(N-benzoxazolin-2-one)acetic acid (BAA) are prepared by changing the temperature of its crystallization from solution in ethanol. Crystallographic data of the α-form are determined: a = 12.7769(17) Å, b = 8.2574(9) Å, c = 16.7390(19) Å, β = 105.087(13)°, space group C2/c, V = 1705.2(4) ų, and Z = 8, while those of β form are a = 5.2854(4) Å, b = 5.9880(4) Å, c = 13.4509(5) Å, β = 94.666(4)°, space group P2₁, V = 424.30(4) ų, and Z = 2. It is found that BAA molecules of the α form combine into infinite one-dimensional chains arranged along axis b by means of O?H···O and C?H···O hydrogen bonds, and these chains are crosslinked via C?H···O hydrogen bonds to form a threedimensional structure. The β form has another system of hydrogen bonds, one of which is bifurcated (O4···O2, O4···O3), and the π–π-interactions between the benzoxazolinone fragments of BAA molecules combined into a chain also arranged along axis b are observed. Calorimetric analysis shows that the polymorphic transition from the α form to the β form occurs at 129°C.     

Reaction of deoxyvasicinone with organolithium compounds

4-Butyl-4-hydroxydeoxypeganine was prepared by lithiation of deoxyvasicinone. Deoxypeganine and 1,2-dihydrodeoxypeganine were produced by reduction of deoxyvasicinone with lithium aluminum hydride.     

Field emission of electrons from cathodes made of carbon fibers with a nanostructured emitting surface

Field electron emission from cathodes made of a bunch of carbon fibers under the condition of technical vacuum is studied experimentally. A model to optimize the field emission properties of the cathode by optimizing its macrogeometry with regard to the emitting surface structure is suggested. The current-voltage characteristics of the cathode are taken in the working voltage range 1–3 kV and for anode-cathode spacings varying from 1 to 10 mm. The current density from the cathode may reach 10 A/cm² or more.     

Bases of exponentials in the spaces Ep(Dn) on a poly-polygon and the representation of the functions from this class in the form of sums of periodic functions

For the spaces E^p(Dⁿ) of functions, defined on the Cartesian product of convex polygons, it is established that a system of exponentials of a special type forms a basis. The dependence of the exponents on the vertices of the polygons is indicated.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 42, No. 3, pp. 324–332, March, 1990.     

Effect of the Catalyst Nature on the Structure of Products of the Reaction of 4-(Dibromomethyl)Benzaldehyde with Trialkyl Orthoformates

Reactions of 4-(dibromomethyl)benzaldehyde with trialkyl orthoformates in the presence of both Brønsted (H₂SO₄) and Lewis (ZnCl₂) acids involved acetalization of the aldehyde group. In the first case, the corresponding acetal is formed as the only product, whereas in the second case the reaction is accompanied by transformation of the dibromomethyl group to give terephthalaldehyde and its mono- and bis-acetals.     

One-pot catalytic synthesis of crown-like macroheterocycles

An efficient procedure has been developed for the synthesis of crown-like N-cycloalkyl-1,5,8-trithia-3-azacyclodecanes and N-cycloalkyl-1,11-dioxa-4,8-dithia-6-azacyclotridecanes by recyclization of saturated oxathiacycloalkanes with carbocyclic amines in the presence of SmCl₃ · 6 H²O as catalyst.