The Crystal Structure of Some Organic Acids

Sim, George A (1955) The Crystal Structure of Some Organic Acids. PhD thesis, University of Glasgow.

Abstract

The crystal structures of some organic acids have been examined by X-ray diffraction methods. Benzoic acid is monoclinic, space group p2 1/c, with four molecules per unit cell. The crystal, structure has been accurately determined from a study of projections of rho0 and (rho0-rhoc) along the a and b axes. The molecules occur as planar, centrasymmetrical dimers, with hydrogen bonds of length 2.64 A between the adjacent carboxyl groups. The hydrogen atoms bonded to the benzene carbon atoms have been clearly revealed in difference syntheses but the carboxyl hydrogen has proved difficult to locate. Corrections have been made for the anisotropic thermal vibration of many of the atoms. Bond length variations in the benzene ring have been found and are discussed. The analysis has been carried out with both visually estimated and Geiger-counter measured intensities and the results obtained with each are compared. 11-amino-undecanoic acid hydrobromide is monoclinic, space group A2/a, with eight molecules per unit cell. The atomic coordinates have been derived from a study of projections of rho0 and (rho0-rhoc) along the a and b axes. Dimeric association between adjacent carboxyl groups occurs and the water molecules, situated on twofold axes, are involved in hydrogen bonding with the Br- and NH+3 ions. The average distance between two alternate cartoon atoms in the hydrocarbon chain is 2.563 A, and the average C-C bond length is 1.539 A, the estimated standard deviation of these values toeing 0.013 A. The hydrocarbon chain is planar tout the terminal nitrogen atom is displaced from this plane. Alternate hydrocarbon chains are inclined in opposite directions and cross each other. Expressions have been derived giving the fraction of reflexions for any particular structure which are determined in sign by a heavy atom or by a group of atoms. In the case of 11-amino-undecanoic acid hydrobromide hemihydrate it was found possible to make an accurate prediction of the fraction of reflexions which have the same sign as the appropriate bromine contribution. Isopalmitic acid is triclinic, space group P1, with two molecules in the unit cell. Electron-density projections along the a axis have been prepared and approximate coordinates for the oxygen and carbon atoms have been estimated.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Organic chemistry
• Date of Award: 1955
• Depositing User: Enlighten Team
• Unique ID: glathesis:1955-79171
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 05 Mar 2020 11:34
• Last Modified: 05 Mar 2020 11:34
• URI: https://theses.gla.ac.uk/id/eprint/79171