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A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Science in Chemistry, University of Regina. xi, 73 p. The objective of this thesis is to examine the performance of Continuum Solvation Models (CSMs) for the quantum chemistry prediction of the thermodynamics of an entropy-dominated reaction. The chelation reaction Zn(NH3)42+ + 2 en Zn(en)22+ + 4 NH3 (en = 1,2-ethylenediamine) is the chosen reaction. Quantum chemistry calculations of the reaction free energy, enthalpy and entropy are performed, and results analyzed, in Chapter 3. The prediction of the aqueous thermodynamic values for this reaction is further complicated by the presence of several conformers of ethylenediamine in 1 M aqueous solutions, and conflicting literature claims over which conformers are most stable. Therefore, for Chapter 2 I first perform quantum chemistry Raman spectra predictions to re-analyze known Raman spectra. I conclude that both trans and gauche conformers of ethylenediamine are present in both liquid and aqueous phases, in contrast with former literature claims that only one of these conformers is preponderant. This identification of low-lying conformers improves the computation of the Gibbs energy of en for the chelation reaction studied in Chapter 3. The conclusion is that conventional CSMs are not accurate enough to properly reproduce the chelate effect. Efforts are then made to account for and correct the error. The approaches I adopt to cure this error include: semicontinuum approach, using a better electronic structure method, better accounting for the internal rotation of the reaction species and changing from the conventional CSMs to others. The major improvement from these approaches is a change in the CSM from the default to a common alternative but with an increased continuum cavity volume. Student yes |
