2020-05-05

Theoretical modeling of organic synthesis is a powerful tool and leads to further insight into chemical systems. Computational chemistry allows obtaining the potential energy surface that experimentally cannot be observed, in addition to transition state calculations, which lead to better understanding the reactivity of an organic synthesis work. In the present thesis, theoretical methods will be used to examine the reaction mechanism paths, structural geometries, transition states, stereoselectivity, regioselectivity, thermodynamic parameters and Fukui functions of some cycloaddition reactions. In the thesis work by means of computational approaches, we studied certain [2+2], [4+2] and [3+2] cycloaddition reactions mainly applying density functional theory (DFT) method with different basis sets. The mechanistic aspects of the reaction paths were investigated in a concerted and stepwise fashion to predict the regioselectivity and stereoselectivity of those cycloadducts.

2012-12-12

Ozonation of methyl orange (MO) in aqueous solution was investigated using ozone in the presence and absence of multi-walled carbon nanotube (MWCNT) as a catalyst. The operating conditions were initial ozone concentrations (2-8 g/m3 NTP), initial MO concentrations (10-40 mg/L), pH (2-9), and amounts of carbon nanotubes (5-20 mg/L). Ozonation of MO in the absence of catalyst was slow. The initial ozone concentration and catalyst dosage exerted positive effects on the removal of MO by ozonation with and without MWCNTs catalyst. However, the initial MO concentration negatively affects MO removal for both systems. The maximum removal efficiency of MO was obtained with its initial concentration of 10 mg/L. The removal efficiency of MO increased with the pH value in the range of 2-3, while a reverse trend was observed when the pH increased from 3 to 9. The influence of pH value indicated that the adsorption of MO on the surface of carbon nanotubes (CNTs) was necessary for its effective degradation by CNTs catalytic ozonation. It was found that, to describe MO adsorption isotherm on CNTs surface, Langmuir isotherm was the most appropriate. The results show that the removal rate of MO was slower than without radical scavenger (sodium bicarbonate). This suggested that removal of MO proceeds through both ozonation reactions, direct and indirect. The inhibition of sodium bicarbonate on the CNTs activity at pH 7 was more significant as compared with the pH value of 3.