The experimental and AB initio studies of the photolysis of selected tribromo-compounds and the water assisted dehalogenation reactions of selected isotribromo-compounds

• Main Authors: Yeung, Chi-shun, 楊智淳
• Other Authors: Phillips, DL
• Language: English
• Published: The University of Hong Kong (Pokfulam, Hong Kong) 2014
• Subjects: Halogenation; Photochemistry; Organohalogen compounds
• Online Access: http://hdl.handle.net/10722/206479

The photochemistry of several tribromo-compounds, R−CBr3 (R = CH2OH, CH2OC(O)CF3, COOH) have been studied by utilizing nanosecond transient absorption (ns-TA) and femtosecond transient absorption spectroscopy. Femtosecond transient absorption experiments showed that isomer species R−CBr2−Br were formed after excitation of R−CBr3 within several picoseconds. The absorption band of the isomers R−CBr2−Br showed a strong solvent dependence upon changing the solvent from cyclohexane to acetonitrile. The absorption wavelength of the proposed isomer intermediates and the spectral shift in cyclohexane and acetonitrile were consistent and supported by results from time-dependent density functional theory (TDDFT) calculations. The decay of the isomer intermediates were significantly shortened by the presence of water and alcohols which indicated that R−CBr2−Br intermediates are likely to react with water and alcohols. Second-order Møller-Plesset perturbation theory (MP2) calculations were employed to investigate the structures and energies of the OH-insertion reactions of R−CBr2−Br when water/alcohol molecules (up to three) were explicitly involved in the reaction complex. The reaction mechanisms examined were found to be dramatically catalyzed by the hydrogen bonding of the water molecules causing the molecule to undergo decomposition. The calculations indicate that the isomer species are able to react with water and alcohol via a water catalyzed OH-insertion/HBr elimination reaction to produce a R−CBr2(OH) product. The ab initio calculations suggested that the R−CBr2(OH) product can undergo a similar water catalyzed reaction mechanism to form R−C(O)Br. The acyl bromide type compounds were also studied using ab initio calculations. The dependence on the substituent group R was found to influence the decomposition pathways that form various final products. The results of the experimental and computational results discussed in this thesis were summarized and some issues were detailed that could be prospects for further study in the future. === published_or_final_version === Chemistry === Doctoral === Doctor of Philosophy