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Abstract In the current work, we have performed computational studies on thermodynamics and kinetics unimolecular and bimolecular decomposition reactions of 1,2-ethanediol monoacetate. In the latter case, methyl radical (•CH3) was used. All calculation were carried out using high level ab initio (CBS-QB3, G3MP2) and density functional theory (DFT) (BMK/6- 31+G(d, p) methods. The results were compared with n-butanol and ethyl acetate data to examine the consequence of presence of the ester group. The thesis consists of three chapters as follows: Chapter 1 presents introduction of different categories of energy resources, non- renewable and renewable energy resources. Using of nonrenewable sources as fuels became limited in many countries because of gases emission. Various forms of renewable energy sources were discussed. Biofuels represent one of the promising renewable energy resources. Among different biofuel compounds, bioalcohols, bioesters and biodiesel were reviewed. Small bioalcohols like biomethanol and bioethanol have many defects as biofuels such as low internal energy, high vapor pressure, low boiling point, , high vapor pressure and some of them has a toxic properties. Those lead to emission large quantities into environment. Recently, researchers have developed many chemical techniques to produce ethylene glycol from biomass. Ethylene glycol is viscous liquid used as a coolant for automotive engines and characterized by high viscosity, low melting point -13 °C, high hydrophobicity, and toxicity. Production of 1,2-ethanediol monoacetate could be prepared from ethylene glycol in acetic acid solution containing LiNO3 and Pd(OAc). 1,2-ethanediol monoacetate has many advantages over lower alcohols, and ordinary esters such as high internal energy, low water absorption, low toxicity, high boiling point, besides providing easiest and fastest H-abstraction. So, it can easily decomposed at both atmospheric and combustion regime. Therefore, our attention in this work was paid to 1,2-ethanediol monoacetate decomposition as model biofuel because of expected good ignition behavior due to its high oxygen content, low vapor pressure, high internal energy compared to its constituents. Chapter 2 gives a short background on quantum chemical calculations and a detail description of the procedures used throughout this work. Geometry optimizations have been performed at the BMK/631+G (d, p) levels of theory. For all stationary points we have carried out frequency calculations at the same level to characterize their nature as minima or transition states and to correct energies for zero-point energy and thermal contributions. IRC calculations carried out at BMK/6-31+g (d, p). Ab initio multilevel (CBS-QB3, G3MP2) procedures also have been used to obtain more accurate results. Chapter 3 presents results and discussion which can be summarized as follows: 1,2-ethanediol monoacetate has four conformers with high stability of M3 conformer due to intra-molecular hydrogen bond (IHB) relative to the rest of configurations. Bond dissociation energies (BDEs) of 1,2-ethanediol monoacetate at CBSQB3 show the following: 1. The Cα-Cβ and Cβ-O bonds are the weakest bonds and have comparable strength. 2. O-H alcoholic bond is strongest bond 107.23 kcal/mol. 3. The C-H bonds strengths of 1,2-ethanediol monoacetate follow the order Cα- H < Cδ-H < Cβ-H. 4. Enthalpies of formation from isodesmic equations at BMK/6- 31+G(d, p) and atomization energies at CBS-QB3 level give the most accurate results when compared with the available experimental data and gives confidence on the unknown value. Pyrolysis of 1,2-ethanediol monoacetate can proceed through either complex or simple decompositions. The first type represents reactions, which precedes through cyclic transition states, while the second type includes simple fission of bonds to produce radicals. This work investigated sixteen channels for 1,2-ethanediol monoacetate decomposition including seven H-transfer reactions and nine simple bond fission reactions. Potential energy diagram indicates that the formation of acetic acid and vinyl alcohol represents the most thermodynamically and kinetically preferable reaction until 400 K. After that, production of vinyl acetate becomes the main channel. The calculated enthalpies of formation for 1,2-ethanediol monoacetate and its radicals show a good agreement with the available experimental data. All of the 113 investigated channels are endothermic and the degree of endothermicity depends of the type of reaction. Rate constants calculations for all channels at different temperatures were computed using the transition state theory (TST) in conjunction with Wigner correction. Bimolecular oxidation of 1,2-ethanediol monoacetate using methyl radical (•CH3) has been done. Thermochemistry and kinetics of 1,2- ethanediol monoacetate oxidation has been studied using density functional theory BMK/6-31+G(d,p) and ab initio CBS-QB3 calculations. Oxidation by methyl radical (•CH3)of 1,2-ethanediol monoacetate occurs through H-abstraction reactions. 1,2-ethanediol monoacetate has four positions for H-abstraction (alpha, beta, delta, and alcoholic position). Comparison has been done between1,2-ethanediol monoacetate results and with n-butanol and ethyl acetate results. The comparison between between1,2-ethanediol monoacetate oxidation and with n-butanol and ethyl acetate oxidation by methyl radical (•CH3) shows the effect of structures from one to other. 1,2-ethanediol monoacetate could function as a biofuel because of its physical properties and decomposition pattern that is comparable to alcohols and esters. |