Browsing by Author "Coetzee, Anita"

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    Structure and decomposition of diol inclusion compounds
    (1998) Su, Hong; Coetzee, Anita
    The inclusion properties of the host, trans-9, 10-dihydroxy-9, 10-diphenyl-9,10- dihydroanthracene, with various guest molecules, namely cyclohexanone, 2- methylcyclohexanone, 3-methylcyclohexanone and 4-methylcyclohexanone, were investigated. The host to guest ratios were determined by programmed temperature thermogravimetry. Two of the four molecular structures were elucidated using single crystal X-ray diffraction. All the inclusion compounds were also characterised by differential scanning calorimetry, hotstage microscopy and Xray powder diffraction. The kinetics of decomposition of the inclusion compound containing the guest cyclohexanone were studied using different experimental techniques under isothermal conditions: these were the quartz microbalance, the levitating balance and isothermal thermogravimetry. The kinetics of decomposition of the other three compounds were studied by means of isothermal thermogravimetry. The Arrhenius parameters determined showed a compensation effect between the activation energies and pre-exponential factors. Competition experiments were performed to determine the selectivity of the host for the four guest substances.
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    Structure and reactivity of selected inclusion compounds
    (1996) Coetzee, Anita; Nassimbeni, Luigi R; Caira, Mino R
    Selected inclusion compounds of hydroxy hosts from three different classes were investigated. The host compounds in class A are 2,7-substituted 2,2'-bis(9-hydroxy-9-fluorenyl)biphenyls, with the substituents being Cl, Br or tert-butyl. They readily form inclusion compounds with a wide variety of solvents. Their inclusion compounds with 1 ,4-dioxane, 1 ,3-dioxane, 1 ,3-dioxolane and acetone were investigated. The crystal structure of an unsolvated, α-phase, of the host compound 2,2'-bis(2,7-dichloro-9-hydroxy-9-fluorenyl)biphenyl was elucidated. The host compounds in class B are modified dihydroanthracenes. The inclusion compounds of trans-9, 1 0-dihydroxy-9, 1 0-diphenyl-9, 1 0-dihydroanthracene with 1,3-dioxolane, trans-9, 1 0-dihydroxy-9, 1 0-di-a-naphtyl-9, 1 0-dihydroanthracene with 1 ,3-dioxolane and with benzene, as well as trans-9, 1 0-dihydroxy-9, 1 0-di-p-tertbutylphenyl-9,10-dihydroanthracene with methanol and with benzene, were studied. The host in class C, 2,2'-bis(diphenylhydroxymethyl)-1, 1 '-biphenyl (H), is similar to the host compounds in class A, but is rendered conformationally more flexible. It forms two structurally similar inclusion compounds, H·H₂0·1/6 C₆H₆ and H-21/₆H2₂.The crystal structure of a p-xylene inclusion compound was also elucidated. The crystal structures of all these inclusion compounds were elucidated. All the compounds were characterised using thermal analysis and X-ray powder diffraction. The kinetics of desolvation of all the inclusion compounds in class A and B were studied, using isothermal or programmed temperature thermogravimetry. Attempts were made to describe the kinetic behaviour in terms of the crystal structures of these compounds. The Arrhenius parameters for the desolvation of all the inclusion compounds under investigation were found to show the compensation effect. The kinetics of solvation of trans-9, 1 0-dihydroxy-9, 1 0-diphenyl-9, 1 0-dihydroanthraceneand 1, 3-dioxolane was studied, using a quartz microbalance designed especially forth is purpose.