Type of Document Dissertation Author Tam, Mary Christina Author's Email Address email@example.com URN etd-04242006-152120 Title Ab initio Calculations of Optical Rotation Degree PhD Department Chemistry Advisory Committee
Advisor Name Title Crawford, Daniel T. Committee Chair Morris, John R. Committee Member Tanko, James M. Committee Member Tissue, Brian M. Committee Member Yee, Gordon T. Committee Member Keywords
- coupled cluster theory
- density functional theory
- optical rotation
Date of Defense 2006-04-18 Availability unrestricted AbstractCoupled cluster (CC) and density functional theory (DFT) are highly regarded as robust quantum chemical methods for accurately predicting a wide variety of properties, such as molecular structures, thermochemical data, vibrational spectra, etc., but there has been little focus on the theoretical prediction of optical rotation. This property, also referred to as circular birefringence, is inherent to all chiral molecules and occurs because such samples exhibit different refractive indices for left- and right- circularly polarized light. This thesis focuses on the theoretical prediction of this chiroptic property using CC and DFT quantum chemical models. Several
small chiral systems have been studied, including (S)-methyloxirane, (R)-epichlorohydrin, (R)-methylthiirane, and the conformationally flexible molecules, (R)-3-chloro-1-butene and
(R)-2-chlorobutane. All predicted results have been compared to recently published gas-phase cavity ringdown polarimetry data. When applicable, well-converged Gibbs free energy differences among confomers were determined using complete-basis-set extrapolations of CC energies in order to obtain Boltzmann-averaged specific rotations. The overall results indicate that the theoretical rotation is highly dependent on the choice of optimized geometry and basis set (diffuse functions are shown to be extremely important), and that there is a large difference between the CC and DFT predicted values, with DFT usually predicting magnitudes that are larger than those of coupled cluster theory.
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