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Title: The crystal and molecular structure of pentacene and hexac (Part 1) and of some derivatives of tropolone (Part 2)
Author: Campbell, Robert Baillie
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1952
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Abstract:
The crystal structures of the polycyclic aromatic hydrocarbons pentacene and hexacene have been determined by X-ray analysis. Pentacene is triclinic, space-group P1-, with two centro-symmetric molecules per unit cell. The molecular arrangement is similar to that in tetracene and to that in monoclinic anthracene. Although 19 carbon atoms out of 22 in the asymmetric unit are resolved in the ( Okl ) projection attempts to refine the structure by two-dimensional Fourier series methods have failed. Hexacene is also triclinic, space-group P1-, with two molecules per unit cell. The crystal structures of the hydrocarbons are closely similar to each other and to those of the preceeding members of the homologous series. A two-dimensional analysis of alpha-monobromotropolone has been carried out. alpha-Monobromotropolone is orthorhombic, space-group P21 21 21, with four molecules per unit cell. A Patterson analysis determined the positions of the four bromine atoms in the (hkO) projection. This was followed by two-dimensional Fourier syntheses and in the final projection all the atoms are clearly resolved. Bond lengths have not been worked out because the tropolone ring appears to deviate slightly from a planar heptagon. This deviation may be due to a steric effect of the large bromine atom or the deviation may be a spurious effect resulting from the effect of the heavy bromine atom on the measured intensities. An approach distance of length 3.05 A. occurs between oxygen atoms of two different molecules and might provide a basis for identifying these oxygens as hydroxyl oxygens. An analysis of cupric nootkatin has been accomplished, also in two dimensions only, by making use of the phase-determining power of the copper atom. Cupric nootkatin is monoclinic, space-group P21/a, with two centro-symmetric molecules of the co-ordination complex per unit cell. In the final projection, made by the usual Fourier series method, only 6 carbon atoms out of the 15 carbon atoms and 2 oxygen atoms in the asymmetric unit are resolved. It has proved possible, however, to elucidate the unknown aspects of the chemical structure of nootkatin viz. the points of attachment of the two side chains to the tropolone ring. Nootkatin would appear to be beta-isopropyl gamma(3-methyl but-2-enyl) tropolone. Preliminary investigations of the crystal structures of tropolone, tropolone hydrobromide, and ferric tropolone have been made. Tropolone is monoclinic, space-group P21/a, with four molecules per unit cell. Tropolone hydrobromide is monoclinic, space-group P2 1/a, with eight molecules per unit cell. The positions of the bromine atoms in the (hkO) projection have been determined, somewhat approximately because of overlap of the two bromine atoms in the asymmetric unit, by Patterson analysis. Ferric tropolone is monoclinic, space-group Cc, with four molecules of the co-ordination complex per unit cell.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.795453  DOI: Not available
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