Crystal structure oxalic acid

Crystal structure oxalic acid 21110, acetylene dicarboxylic acid 2HiO. 

G. E. Pringle. Acta Cryst. 7, 716-20 (1954). Crystal structure oxalic acid. 

The crystal structure of many compounds is dominated by the effect of H bonds, and numerous examples will emerge in ensuing chapters. Ice (p. 624) is perhaps the classic example, but the layer lattice structure of B(OH)3 (p. 203) and the striking difference between the a- and 6-forms of oxalic and other dicarboxylic acids is notable (Fig. 3.9). The more subtle distortions that lead to ferroelectric phenomena in KH2PO4 and other crystals have already been noted (p. 57). Hydrogen bonds between fluorine atoms result in the formation of infinite zigzag chains in crystalline hydrogen fluoride... 

Working first with Polanyi, Weissenberg, and Brill, and later as the leader of the Textile Chemistry Section, Mark successively published papers on the crystal structures of hexamethylenetetramine, pentaerythritol, zinc salts, tin, urea, tin salts, triphenylmethane, bismuth, graphite, sulfur, oxalic acid, acetaldehyde, ammonia, ethane, diborane, carbon dioxide, and some aluminum silicates. Each paper showed his and the laboratory s increasing sophistication in the technique of X-ray diffraction. Their work over the period broadened to include contributions to the theories of atomic and molecular structure and X-ray scattering theory. A number of his papers were particularly notable including his work with Polanyi on the structure of white tin ( 3, 4 ), E. Wigner on the structure of rhombic sulfur (5), and E. Pohland on the low temperature crystal structure of ammonia and carbon dioxide (6, 7). The Mark-Szilard effect, a classical component of X-ray physics, was a result of his collaboration with Leo Szilard (8). And his work with E. A. Hauser (9, 10, 11) on rubber and J. R. 

The direct reaction of [TCO4] in ethanolic solution with dppe and oxalic acid produces the red Tc" complex [Tc(ox)(dppe)2] (552). Attempts to prepare similar complexes with succinic acid, phthalic acid, or salicylic acid failed, or the complexes were stable in solution only. " Similarly, cationic complexes of Tc" are produced by reaction of the versatile precursor [TcO(OH)(dppe)2] (204) with various dithiocarbamates, which produces several complexes of general formula [Tc(dtc)(dppe)2] (553). For this reaction the reductant formamidine sulphinic acid (510) was required in an alkaline solution. The X-ray crystal structure of [Tc(S2CNMe2)(dppe)2] (554) shows a distorted octahedral geometry. Cyclic voltammetry reveals a reversible reduction wave Tc"/Tc couple at —0.53 V, and a reversible oxidation at +0.3 V for the Tc" /Tc" couple. The same compound (554) was also prepared from the thiourea precursor [TcO(tmtu)4] + (91).The reaction of this precursor in dmf in the presence of dppe produced a mixture of brown [TcO(dtc)(tmtu)2] and the Tc" complex (553). The first compound is probably an intermediate... 

Robertson, J. M., and J. Woodward The Structure of the Carboxyl Group. A Quantitative Investigation of Oxalic Acid Dihydrate by Fourier-Synthesis from the X-Ray Crystal Data. J. chem. Soc. London 1936, 1817-.— — Trans. Faraday Soc. 36, 913 (1940). 

The effect of hydrogen bonds on the physical properties of crystals is shown in a striking way by oxalic acid. This substance exists in two anhydrous crystal forms. 1 One of these, the a form, contains layers of molecules held together by hydrogen bonds, the structure of a layer... 

Similar structures have been found for many other dicarboxylic acids, including succinic acid, COOH(CH ) COOH glutaric acid, COOH(CH ) COOH adipic acid, COOH(CH,) pOOH, and sebacic aoid, COOH(CH )jCOOH. Crystal structure determinations have also been made of many carboxylic acid hydrates in all of the crystals the carboxyl groups form hydrogen bonds, usually with water mole oules. An example is oxalic acid dihydrate in this crystal the 0—H 0 distance is 2.50 A. 

The X-ray crystal structure of protonated formic acid, acetic acid, and methyl formate has recently been determined by Minkwitz and co-workers. In agreement with NMR data discussed above, the nearly equal C—O bond lengths of protonated formic acid (1.239 and 1.255 A),573 protonated acetic acid 275 (1.251-1.291 A for various salts),574 and protonated methyl formate 276 (1.260 and 1.264 A)575 show efficient delocalization of the positive charge. Minkwitz et al.576 have also studied protonation of oxalic acid in HF-SbF5 and isolated the hexafluoroantimonate of the mono- and diprotonated acid at 75°C and 40°C, respectively. Structural characteristics are very similar to those of the other cations discussed. 

Figure 11.5. The face-centered crystal structure of orthorhombic oxalic acid. On the left is the cell projected along the a0 axis. Only one molecule at a corner and three molecules in the centers of the faces are shown for clarity. On the right, a packing drawing shows all molecules in the cell with the same view.

The glandular trichomes are the structures in which the cannabis resin is pro-dnced. These can be fonnd on the underside of the leaves, and occasionally on the stems, but are mainly associated with the flower structures, with female plants being particularly rich in such structures. The unicellular trichomes are found all over the plant, but interestingly, only point up the plant. The cystolithic trichomes are found all over the plant and may have oxalic acid crystals visible within their bases. If aU of these trichomes are found together, then the plant material can be definitively identified as Cannabis saliva, since no other plant displays such a combination [5]. However, some plants possess trichomes which may be confused with those present on Cannabis sativa [6, 7] and care should thus be taken in definitive identification. 

Huang, C.-M. Leiserowitz, L. Schmidt, G.M.J. Molecular packing modes 11. Crystal structures of 2-1 complexes of benzamide with succinic acid and furamide with oxalic acid. J. Chem. Soc., Perkin Trans. 1973, 2, 503-508. 

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