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X-ray crystallographic studies of four organic compounds Hughes, David Lewis


Single crystal X-ray diffraction methods have been used to investigate four organic compounds, two monosaccharide derivatives and two nitrobenzene compounds: 1. methyl 3-C-(carbomethoxymethyl)-4,6-di-O-p-chlorobenzoyl-2,3- dideoxy-α-D-ribo-hexopyranoside, C(24)+H(24)+C(12)O(8); 2. 5-0-(p-bromobenzenesulphonyl)-2,2'-O-cyclohexylidene-3-deoxy-2-C- hydroxymethyl-D-erythro-pentono-1,4-lactone, C(18)H(21)BrO(7)S; 3. 2,6-dichloro-4-nitroaniline, C(6)H(4)Cl(2)N(2)O(2); 4. ethyl 3,5-dinitrobenzoate, C(6)H(8)N(2)O(6). Crystals of the di-(p-chlorobenzoate) derivative of a novel branched-chain sugar, methyl 3-C-(carbomethoxymethyl)-2,3-dideoxy-α-D-ribo-hexopyranoside, are monoclinic, space group, P2(1), a = 5•752, b = 15•436, c = 13•698 Ǻ., Β = 93•74° and Z = 2. Intensity data have been measured on an automatic diffractometer, firstly with Mo-K(α) radiation, then more accurately with Cu-K(α) radiation. Efforts to confirm the molecular structure of the derivative have been unsuccessful, although various methods of analysis have been employed; the principal approaches have been the examination of the Patterson and sharpened Patterson maps, and by direct methods, the application of the tangent formula in the phase determination procedures for noncentrosymmetric space groups. None of the methods has produced any encouraging, distinctive portions of the molecule, and at present, the investigation has been halted. The structure of "a"-D-isosaccharinic acid has been determined by crystal structure analysis of a derivative which was shown to be 5-0-(p-bromo-benzenesulphonyl)-2,2'-0-cyclohexylidene-3-deoxy-2-C-hydroxymethyl-D-erythro-pentono-l,4-lactone. Crystals are monoclinic, a = 5•757, β = 10•586, c = 16•021 Ǻ., 8 = 98•85°, Z = 2, space group P2(1). The intensities of 1319 reflections were measured with a scintillation counter and Cu-K(α) radiation, the structure was derived from Patterson and electron-density maps, and refined by least-squares methods, the final R being 0•10 for 1140 observed reflections. The absolute configuration is established, since the compound was obtained by degradation of cellulose. Each of the two five-membered rings in the derivative has an envelope conformation, with one atom displaced from the plane of the other four .In the 1,3-dioxolane ring, the displacement is 0•49 Ǻ.; the γ-lactone ring is less prominently bent, with displacement only 0•14 Ǻ. The bond distances and valency angles in the molecule do not differ significantly from the usual values, and the intermolecular distances correspond to van der Waals' interactions. Crystals of 2,6-dichloro-4-nitroaniline are generally twinned; they are monoclinic, space group P2(1)/c, a = 3•723, b = 17•833, c = 11•834 Ǻ., 8 = 94•12°, Z = 4. Intensity data were collected for one of the twins on an automatic diffractometer. The coordinates of the two chlorine atoms were found in a Patterson map and all the other atoms in electron-density and difference Fourier maps. The structure was refined by full-matrix least-squares methods to R = 0•038. There are only slight deviations from overall planarity of the molecule, the amino and nitro groups being rotated by 6•3 and 7•2° respectively out of coplanarity with the benzene ring. The amino group appears to be held nearly coplanar with the benzene ring by intermolecular N-H...0 and intramolecular N-H...C1

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