Photolytic Studies of Aryl and Heteroaryl Nitrenium Ions: Laser Flash Photolysis Studies
| dc.contributor.advisor | Falvey, Daniel E | en_US |
| dc.contributor.author | Thomas, Selina Ivan | en_US |
| dc.contributor.department | Chemistry | en_US |
| dc.contributor.publisher | Digital Repository at the University of Maryland | en_US |
| dc.contributor.publisher | University of Maryland (College Park, Md.) | en_US |
| dc.date.accessioned | 2006-09-12T05:31:19Z | |
| dc.date.available | 2006-09-12T05:31:19Z | |
| dc.date.issued | 2006-05-07 | en_US |
| dc.description.abstract | The objective of the thesis was to understand the chemical and kinetic behavior of arylnitrenium ions and a heteroaromatic nitrenium ion through photolytic studies. <em>N</em>-(4,4'-dichlorodiphenyl) nitrenium ion and <em>N</em>-(4,4'-dibromodiphenyl) nitrenium ion are the halogenated counterparts of diphenylnitrenium ions and are generated photochemically from their respective <em>N</em>-(4,4'-dihalogenated diphenylamino)-2,4,6-trimethylpyridinium tetrafluoroborate salts. The halogenated diarylnitrenium ions are ground state singlets that live for more than 1 x 10<sup>5</sup> ns in acetonitrile. In the absence of nucleophiles, these ions decay to form a dimerized hydrazine. These ions react with nucleophiles such as water and alcohol at a rate constant of 10<sup>4</sup> - 10<sup>5</sup>M<sup>-1</sup>s<sup>-1</sup> and at diffusion limit with chlorides. With arenes, these ions react via electron transfer mechanism and nucleophilic addition process. The rate constants for the electron transfer mechanisms are between 10<sup>5</sup> - 10<sup>9</sup> M<sup>-1</sup> s<sup>-1</sup> and depend on the Eox of the arenes. Arenes with Eox above 1.78 V showed no reactivity towards the ion. Unlike other diarylnitrenium ions, the halogenated diarylnitrenium ions react with hydrogen atom donors via a hydrogen atom transfer mechanism. The triplet behavior of these ions is attributed to singlet-triplet intersystem crossing facilitated by the lower singlet-triplet energy gap. Therefore, it has been concluded that substituting halogens in diphenylnitrenium ion lowers the singlet-triplet energy gap and increases the lifetime of these ions. (<em>N</em>-Methyl-<em>N</em>-4-biphenylyl) nitrenium ion generated by photolysis was reacted with amino acids and proteins to determine their reactivity with these ions. Eight amino acids were observed to react with the ion at a rate constant of 10<sup>7</sup> - 10<sup>9</sup> M<sup>-1</sup> s<sup>-1</sup>. The rate constants depend on the nucleophilicity of the side chains of the amino acids. In addition, this ion also reacts rapidly with proteins with a rate constant of 10<sup>8</sup> M<sup>-1</sup> s<sup>-1</sup>, comparable to their reactions with ss-DNA. Investigations on generating the quinoline <em>N</em>-oxide nitrenium ions showed that the transient species from the photolysis of 4-azidoquinoline <em>N</em>-oxide (4-AzQO) shows more characteristics of a nitrenium ion. The formation of 4-aminoquinoline <em>N</em>-oxide upon photolysis of 4-AzQO in acetonitrile with 10% sulphuric acid and the electron transfer reactions observed with arenes, indicate that the transient species generated could be a heteroaromatic nitrenium ion. However, more experiments are needed to confirm the assignment. | en_US |
| dc.format.extent | 1345629 bytes | |
| dc.format.mimetype | application/pdf | |
| dc.identifier.uri | http://hdl.handle.net/1903/3690 | |
| dc.language.iso | en_US | |
| dc.subject.pqcontrolled | Chemistry, Organic | en_US |
| dc.subject.pquncontrolled | Nitrenium ion | en_US |
| dc.subject.pquncontrolled | Photochemistry | en_US |
| dc.subject.pquncontrolled | Arylnitrenium ion | en_US |
| dc.subject.pquncontrolled | Amino Acids | en_US |
| dc.subject.pquncontrolled | Proteins | en_US |
| dc.subject.pquncontrolled | Quinoline N-oxide nitrenium ion | en_US |
| dc.title | Photolytic Studies of Aryl and Heteroaryl Nitrenium Ions: Laser Flash Photolysis Studies | en_US |
| dc.type | Dissertation | en_US |
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