M.Sc. / Molecules containing a long saturated carbon chain are present in many natural and commercial products. Due to the conformational flexibility of the carbon chain, different molecular conformations of these molecules are possible resulting in polymorphism. The crystal structure of a material greatly influences its chemical and physical properties, leading to different properties for different polymorphs. Designing materials with specific properties requires the understanding of the underlying fundamental parameters and forces influencing the packing of molecules in the crystal. A thorough literature study was conducted to determine the crystallographic research that has been done long chain compounds. Not only did this literature study lead to the identification of possible research fields, but also provided a solid background concerning the crystallographic behavior of these systems. In this project we investigated the polymorphism of simple molecules containing a saturated carbon chain with seventeen or eighteen carbons. Two systems are investigated namely n-alkylammonium halides and esters of fatty acids. By varying crystallization conditions different polymorphs of each compound can be obtained. Various experimental techniques were employed to shed light on the structure and packing of the long chain molecules in the different polymorphs. The crystal structure of the low temperature polymorph of n-octadecylammonium bromide was determined, as well as the cell dimensions of the low temperature form of noctadecylammonium chloride. The unit cell dimensions of n-octadecylammonium iodide monohydrate was also determined. The structures of the methyl and ethyl esters of noctadecanoic acid and the symmetrical -ester heptadecyl-heptadecanoate was investigated. In this project a young, dynamic research field was investigated. This led to the identification of other possible fields of study. Because there are not many reports in the literature on the crystallographic characteristics of these compounds, the evolving of the project required a lot of creativity.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uj/uj:3249 |
| Date | 27 August 2012 |
| Creators | Rademeyer, Melanie |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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