| dc.contributor.author | Ortiz Ojeda, Wendy. | en_US |
| dc.date.accessioned | 2014-10-21T12:36:16Z | |
| dc.date.available | 2001 | |
| dc.date.issued | 2001 | en_US |
| dc.identifier.other | AAINQ66654 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55783 | |
| dc.description | Zeolites are microporous materials capable of hosting organic molecules within their internal voids. Although considerable research has been directed towards understanding chemical transformations that occur within these structures, the fundamental role played by zeolites in promoting or controlling these transformations is still not well understood. The present doctoral project has involved the study of reactive intermediates within the internal voids of zeolites in order to enhance our understanding of such supramolecular systems and their effect on the reactivity of transient intermediates. Time-resolved nanosecond diffuse reflectance has been employed to systematically study the effect of zeolite composition on the dynamics of organic radical reactions. | en_US |
| dc.description | The effect of zeolite environment on ionization reactions was examined to determine and quantify the internal ionizing power of various zeolites. In particular, the investigation focused on studying the kinetics of heterolysis reactions of organic radicals containing a leaving group at the beta-position within alkali-metal exchanged Y-zeolites. The kinetic probe molecule, 2-halo-1-(4-methoxyphenylethyl) radical was generated within zeolite supercages upon laser photolysis of a precursor arylethyl acetate. As the rate constant for the cleavage of the carbon-leaving group bond is highly sensitive to the environment of the media, this reaction was well-suited to probe the ionizing power of zeolites. Results show the ionizing power of Y zeolites depends strongly on the nature of the counterion and increases upon going from CsY to LiY (largest to smallest cation). However, the polar environment of zeolites was found to be less ionizing than aqueous conditions but reaction rate constants were similar to values obtained in water/methanol mixtures containing from 30% to 70% water. Interestingly, a significant reduction in the absolute ionizing ability of the zeolite was found when the suprastructure was hydrated. In addition, substrate structure was observed to have a significant role on the reactivity of the beta-substituted radical within zeolites. These results demonstrate the active role played by the zeolite framework in encouraging heterolytic reactions to occur. | en_US |
| dc.description | The reactivity of benzylic radicals generated by laser excitation of arylacetic acids within the cavities of zeolites was also examined. This project resulted in the first direct detection of the benzyl radical and the benzyl anion within cation-exchanged Y zeolites. Absolute rate constants for the reactivity of these types of radicals were obtained and it has been found that the reactivity is highly dependent on the structure of the radical and nature of the zeolite. The investigation revealed radical mobility and steric crowding are important factors in the radical decay mechanism. For example, the cumyl radical is less mobile within the zeolite framework than the smaller benzyl radical. As a result, it is less able to move and decays slower than the benzyl radical. Furthermore, each of these two similar radicals decay via different decay mechanisms in zeolites. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2001. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Chemistry, Organic. | en_US |
| dc.title | Study of reactive intermediates within nonacidic zeolites: beta-heterolysis and radical reactivity. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
