Ab initio study on the structures, energetics and reactivity of some chemical systems
Student thesis: Doctoral Thesis
In this thesis, the first part focuses on high-level theoretical predictions for the thermochemical properties of (i) thiophene, furan, pyrrole, 1,3-cyclopentadiene, borole and their cations (C4H4X/C4H4X+, X = S, O, NH, CH2 and BH); (ii) cyclopentadienyl radical/cation/anion (C5H5/C5H5+/C5H5-); and (iii) sulfur tetroxide neutral/anions and their protonated forms (SO4/SO4-/SO42-, HSO4/HSO4- and H2SO4) using the wavefunction-based ab initio CCSD(T)/CBS or CCSDT/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled-cluster level with single, double excitations plus a perturbative triple excitations [CCSD(T)] or a full triple excitation (CCSDT). The comparisons between the coupled-cluster predictions and the experimental data suggest that the CCSD(T)/CBS (CCSDT/CBS) procedure is capable of providing accurate ionization energy, electron affinity and heats of formation values with an uncertainty of ≈4 kJ/mol. The second part is to study the mechanisms for (i) epoxidation of ethene with hydrogen peroxide catalyzed by a manganese(V) nitrido complex; (ii) Lewis acid-activated oxidation of alcohols by permanganate (MnO4-); (iii) Lewis acid-activated oxidation of cyclohexane catalyzed by ruthenium tetroxide (RuO4), perruthenate anion (RuO4-) and trichlorodioxoruthenate anion (RuO2Cl3-); (iv) oxygen evolution in water by monoprotonated and deprotonated ferrates (FeO3OH-/FeO42-); and (v) olefin polymerization catalyzed by titanium(IV) pyridine-2-phenolate-6-(σ-aryl) complex, using density functional theory (DFT). The DFT calculations together with the experimental results obtained in the kinetic measurements provide important insights into the mechanisms of above reactions. In the last part, a novel theoretical method is developed to estimate (i) the aromatic stabilization energy (ASE) of aromatic compounds, including benzene (C6H6), naphthalene (C10H8), anthracene (C14H10), phenanthrene (C14H10), chrysene (C18H12), triphenylene (C18H12), picene (C22H14), benzo[c]picene (C26H16), dibenzo[c,m]picene (C30H18), tetrabenzo[a,c,h,j]anthracene (C30H18) and tribenzo[a,k,u]trinaphthylene (C42H24); and (ii) intramolecular hydrogen bond energy (EIHB) of maleic acid monoanion (cis-HO2CCH=CHCO2-), nitromalonamide (HOH2NC=CNO2CONH2), cysteine monoanion (-SCH2CHNH2CO2H), 2-nitrophenol (2-HOC6H4NO2), 2-hydroxybenzoic acid (2-HOC6H4CO2H), 2-hydroxybenzaldehyde (2-HOC6H4COH), carbonylimine (HN=CHCH2COH) and enolimine (HN=CHCH=CHOH). The electron delocalization in aromatic compounds and hydrogen bond interaction are normally taken as the donor-acceptor interactions of π electrons from π orbital to π* orbitals and of lone electrons from non-bonding orbital to σ*orbital, respectively. Our approach is to construct appropriate hypothetical structures with localized electrons and use the hypothetical structures as a reference to evaluate the ASE and EIHB.
- Quantum chemistry