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UBC Theses and Dissertations

The crystal and molecular structures of some organic compounds. Mak, Thomas Chung Wai

Abstract

The crystal and molecular structure of biphenylene has been refined from normal and generalized projections along the c-axis. The gross features of the structure previously determined have been confirmed. A comparison of the measured bond lengths and those calculated by simple resonance theory and by molecular orbital theory indicates that the latter gives a better description of the electron distribution in the molecule. In terms of the Kekule structures the preferred formulation is that which describes the molecule as a cyclobutane derivative. These conclusions are in agreement with the chemicalibehaviour of biphenylene and its derivatives. An adduct formed by passing carbon monoxide into a solution of mercuric chloride in methanol has been shown by X-ray analysis to be methoxycarbonylmercuric chloride. The coordination around the mercury atom is exactly linear, and the molecule is planar, except for the methyl group, whose carbon atom is displaced by 0.39 Å from the plane of the other atoms. A re-examination of the crystal structure of p-chloronitrobenzene has established that the space group, is not Pa as previously assigned, but P2₁/a which implies a molecular centre of symmetry. Projections along the a- and b-axes indicate that this is achieved by a disordered arrangement of molecules involving random interchange of the positions of the chlorine atom and nitro group. A series of acenaphthene derivatives has been examined by X-rays, and the crystal and molecular structures of acenaphthenequinone, cis-1,2-acenaphthenediol and cis-1,2-acenaphthenediol dinitrate determined with precision. In all three compounds the carbon skeleton is planar, and the strain in the peri-ring is almost entirely taken up by valency-angle distortions, both in the peri-ring and in the naphthalene rings. The variation of bond lengths in the aromatic nucleus is similar to that in naphthalene. The acenaphthenequinone molecule is planar, and the short peri-bonds (average value 1.48 ± 0.01₄Å) are indicative of conjugation between the aromatic rings and the carbonyl groups. The C₁-C₂ bond distance of 1.53±0.02Å agrees well with the value reported for acenaphthene. In cis-1,2 -acenaphthenediol the peri-bonds are significantly shortened (mean length 1.48±0.01₀Å) while the 1.60±0.01₄Å bond distance shows the effect of ring strain and steric repulsion of the non-bonded oxygen,atoms. The crystal structure consists of zigzag chains of intermolecular hydrogen bonds formed between molecules related by a screw axis, the intermolecular 0….0 distances being 2.72 and 2.70 Å. The C₁-C₂bond in cis-1, 2-acenaphenediol dinitrate has a length almost identical to that in the diol. There is no bonding between the nitroxy groups, which are planar and inclined at angles of +62.1° and +71.2° to the plane of carbon atoms.

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