Since the development of the understanding that the electron distribution within a molecule is chiefly responsible for its properties and behavior, factors influencing this charge distribution have been of interest to scientists. The chemical reactivity of a molecule, the physical properties, and to a large extent, structure and geometry, are all functions of the electron distribution. This study examines the issue of electronic structure from two points of view, each of them focussing on a specific component within the molecules studied. In the present work, the effects of the highly polar carbonyl group on spectroscopic parameters and physical behavior are investigated. An additional area of study is the effect of fluorine substitution on the energy levels of some halogenated ethylenes. The specific parameters examined are the ionization potentials, the absorption frequencies, and the energies of a class of excited states known as molecular Rydberg states. It was during the study of these halogenated ethylenes that the observations leading to the carbonyl compound investigations were made, so that the two areas examined are connected both experimentally and chemically.

Dichapetalum cymosum (poison leaf) is a very common problem plant in southern Africa. Fluoroacetic acid, believed to be the poisonous entity in the plant, is produced by the plant, but the micro-organisms associated with this plant may also play a role in the production thereof. A previous study on Burolderia cepacia, an endophyte of D. cymosum showed active metabolism of fluoroacetate by this endophyte. The isolated endophytes from D. cymosum were studied to determine whether they synthesise any fluorinated compounds. It seemed from preliminary results that symbionts might play a role in the synthesis of the poisonous entities in D. cymosum, but further investigation is required. The detection of glandular lesions on the abaxial side of the leaf led to closer examination and the cross sections revealed unusually deformed epidermis cells with adjacent cells containing vacuoles filled with phenolic-like crystals. Transmission electron microscopy (TEM) of the spongy parenchyma cells directly above the glandular lesions indicated the presence of clusters of small, virus-like particles (VLPs) in the chloroplasts. Observations by TEM showed that these VLPs have analogous structures to phytoferritin. Tapura fischeri (leafberry tree) is a tree member of the same family, and it was found to also contain a fluorinated compound. Endophytes were also found in the plant and similar glandular lesions with analogous VLPs were observed at these sites. This might indicate that endophytes have a share in the biosynthesis of the fluorinated compounds found in Dichapetalaceae. Numerous factors ought to be considered in order to fully understand the chemical ecology of the intricate system regarding the endophytes and the possible toxicity of the family Dichapetalaceae. / Dissertation (MSc)--University of Pretoria, 2012. / Plant Science / unrestricted