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The crystal structures of malonamide, cyanoacetamide, a compound C₂₀H₃₃N₃, and acetyltriphenylsilane Chieh, Peter Chung

Abstract

Supervisor: Professor James Trotter The crystal structures of malonamide, cyanoacetamide, a methiodide derivative of a compound, C₂₀H₃₃N₃, and acetyltriphenylsilane have been determined by single crystal X-ray diffraction methods. The first three are organic compounds and the fourth is an organometallic compound. A summary of the crystal data is given below:[data omitted] The cell dimensions and space groups of all the crystals were determined from rotation, Weissenberg and precession photographs and on the General Electric Spectrogoniometer. The intensities of the reflexions of these compounds, except the compound C₂₀H₃₃N₃3, were collected on a General Electric XRD-6 Automatic Spectrogoniometer with scintillation counter, Mo-K∝ or Cu-K∝ radiation and a θ-2θ scan. The intensity data for C₂₀H₃₃N₃ were collected on a G. E. XRD-5 Spectrogoniometer. The crystal structure of malonamide was solved by direct methods. The signs of 158 reflexions with ∣E|≥ 1.50 were derived using the symbolic addition method. The fourteen highest peaks on the three-dimensional E-map corresponded to two molecules of malonamide in the asymmetric unit. With these coordinates, the discrepancy factor, R, was 0.38. The hydrogen atoms were located on a difference Fourier at R=0.12. With all nonhydrogen atoms anisotropic, the refinement was complete at R=0.05, using block-diagonal least-squares methods. The two symmetry-unrelated molecules have different orientations but similar conformations. The amide groups are rotated out of the central C-C-C plane, one by 65° and the other 40°. The mean bond distances are C-C, 1.506A;C-N, 1.317A, C=0, 1.242A, and after correcting for thermal libration, C-N, 1.334A; C=O, 1.254A. The molecules are held together by hydrogen bonds involving all eight amino hydrogens, with each oxygen accepting two hydrogen bonds. The structure of cyanoacetamide was solved by Patterson methods combined with information from electron spin resonance measurements and with considerations of possible hydrogen-bond formation. The structure contains layers of molecules and this reduces the three-dimensional Patterson to a two-dimensional one. The trial structure had a discrepancy of 0.50 and refined to 0.089. Through hydrogen-bonding of the amide group, the two symmetry-unrelated molecules form dimers, which can be considered as packing units, and other units are generated by a screw axis, 2₁. The dimers are bonded to each other by a weak hydrogen bond of the type N-H⃛N≡C. The layers are related to each other by a centre of symmetry. The structures of C₂₀H₃₃N₃•CH₃I and acetyltriphenylsilane were solved by the heavy atom method. The positions of the heavy atoms were obtained from the Patterson functions, and other atoms from consecutive Fourier maps. The compound C₂₀H₃₃N₃ of unknown structure was obtained in an attempted laboratory synthesis of the alkaloid matrine. The structure of the compound was derived by single crystal X-ray structure analysis. Features of the structure are described. In acetyltriphenylsilane the acetyl and three phenyl groups are arranged tetrahedrally around the silicon atom. The phenyl rings are orientated in a propeller fashion and the features of the structure are compared with the germanium analogue.

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