Electron Diffraction Study of the Molecular Structure of 6,6′-bis>(1,5-Diazabicyclo[3.1.0]hexane)

The molecular structure of 6,6-bis(1,5-diazabicyclo[3.1.0]hexane) was investigated by gas-phase electron diffraction using quantum-chemical calculations. Two conformations were found: boat for bicyclic fragments and anti relative to the exocyclic bond.     

Molecular structure of 1,10-dicarba-closo-decaborane(10), 1,10-C2B8H10, by gas-phase electron diffraction

The molecular structure of the title compound has been determined by gas-phase electron diffraction, assuming that the C₂B₈ unit has the form of a bicapped square antiprism (D_4d symmetry). The amplitudes of vibration and the shrinkage corrections were calculated from the force field transferred mainly from 1,6-C₂B₄H₆. The molecular parameters (r_g, φ_α) and uncertainties (3σ) are: B-C = 1.602(2), B2-B3 (basal) = 1.850(5), B2-B6 (equatorial) = 1.829(4), B-H = 1.164(14), C-H = 1.14(2) and ∠C-B-H = 117.5(1.8)°. Comparisons are made with structural data for other carboranes studied in the gas phase.     

Electron diffraction study on the molecular structure of hexamethylcyclotrisilazane, [(CH3)2SiNH]3

A gas electron diffraction study yielded the following geometrical parameters for hexamethylcyclotrisilazane: r(Si-N) = 1.728 ± 0.004 Å, r(Si-C) = 1.871 ± 0.004 Å, r(C-H) = 1.124 ± 0.007 Å, ∠N-Si-N = 108.4 ± 1.0°, ∠Si-N-Si = 126.8 ± 0.8°, ∠C-Si-C = 108.9 ± 2.3°, ∠H-C-H = 111.6 ± 0.9°. The (SiN)₃ ring was found to be puckered but the deviation from planarity is relatively small. Details of the ring shape could not be determined. The degree of ring puckering in six-membered rings with alternating atoms can be roughly predicted from the bond angles in analogous non-cyclic molecules.     

Hypersonic flow past delta wings of a certain class at angle of attack with an attached shock

We study the hypersonic flow of an inviscid ideal gas past a delta wing of small aspect ratio at a finite angle of attack. Increasing the Mach number M of the approaching flow to infinity for a constant geometric parameter characterizing the stream disturbance (for example, the body relative thickness or angle of attack), we obtain the limiting hypersonic flow pattern about the body, when the very strong compression shock approaches close to the body, forming a thin compressed layer of disturbed gas flow. Such a flow may be studied using the method of the small parameter, which characterizes the density ratio across the compression shock [1, 2].In [3,4] an analysis is made of the flow past conical wings whose aspect ratio is of order unity. In this case the compression shock will be attached to the leading edge. In [5] a study is made of the flow past wings of small aspect ratio which diminishes along with the small parameter in such a way that the wing half-apex angle has the same order of magnitude as the Mach cone angle within the compressed layer.In this case the angle of attack remains finite (of order unity) so that as M the hypersonic law of plane sections for slender bodies at large angles of attack [6] is satisfied, which together with the additional limit passage0 leads to the similarity law established in [5]. In this case both the case of the detached shock (when the similarity parameter <2), considered in [5, 7], and the case of the attached compression shock (>2) are possible.The monograph [2] reproduces the results of these studies with certain extensions, and also considers the direct problem of flow past a flat delta plate with attached shock, whose solution was found to contain several singular points which require further investigation.In the present study, considering the inverse problem, we were able to construct a closed pattern of the flow past wings of a certain class with thickness and with an attached compression shock, where the field of the gas-dynamic parameters and the shape of the wing surface and of the shock wave are everywhere continuous and do not contain any singular points with the exception of the known thin entropy layer near the stagnation point, which shows up only in the higher approximations [2, 4].In conclusion I would like to thank V. V. Sychev and V. Ya. Neiland for discussions of the subject and of the results, and I would also like to thank V. P. Kolgan for assistance in making the calculations.     

On the flow around a moving plate by a traveling shock

The incidence of a weak shock on a plate moving at supersonic speed is examined theoretically. The shock overtakes the plate. Cases with constant stream parameters behind the shock front and with a nonuniform stream are considered. Formulas are obtained for the time dependence of the plate lift.Moscow. Translated from Izvestiya Akademii Nauk SSSR. Mekhanika Zhidkosti i Gaza, No. 2, pp. 173–176, March–April, 1972.     

Electron diffraction study of 1,10-dicarbaclosodecaborane(10)

Conclusions The structure of the 1,10-C₂B₈H₁₀ molecule was determined by the electron diffraction method. The following geometric parameters were obtained for the D₄d symmetry model: B-C = 1.60(1) Å; B-B (basal) = 1.87(1) Å; B-B (equatorial) = 1.80(1) Å; B-H = 1.17(3) Å and the C-B-H angle = 13(5.7)°. These data are in good agreement with the structure of the B₁₀H ₁₀ ^2– ion or of the less symmetrical 1,6-C₂(CH₃)₂B₈H₈ isomer.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 438–440, February, 1976.     

Molecular Structure of Silatrane Determined by Gas Electron Diffraction and Quantum-Mechanical Calculations

The geometry of silatrane HSi(OCH₂CH₂)₃N has been determined by gas electron diffraction, ab initio calculations, and vibrational spectroscopy of crystal. Using the scaled force field from DFT calculations the amplitudes and perpendicular corrections were calculated. It was assumed that the silatrane molecule has C ₃ symmetry. The following values (r _g bond lengths in Å and _a bond angles in deg. with three standard deviations from the least-squared refinements using a diagonal weight matrix) are: SiN 2.406(27); NC 1.443(7); OC 1.399(11); SiO 1.648(3); CC 1.504(15); NSiO 78.8(21); SiOC 128.1(11); SiNC 105.4(14); CCO 117.0(26); CCN 108.2(30); CNC 113.2(17); OSiO 116.3(13). The 5-membered rings are flattened. The sum of its bond angles is equal to 537.5(42). It is shown that a very large difference is found for Si—N distance from ab initio and DFT calculating.     

A new method for the synthesis of 2,4-diamino-6-arylpyrimidines

A method for the synthesis of 2,4-diamino-6-arylpyrimidines from guanidine and α-chlorocinnamonitriles was developed. The starting nitriles can be easily prepared by catalytic olefination reaction.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 249–251, January, 2005.