Basis set dependence of ORD and CD spectra

Christopher Rinderspacher, University of Georgia

This research aims at correlating chemical structure with chiroptical properties. Since the operator for optical rotatory dispersion (ORD) does not commute with the Hamiltonian, it is necessary to re-evaluate the usefulness of commonly employed basis sets. As a preliminary result we found that varying single s-type basis functions on just one hydrogen atom bound to the stereogenic center of CHBrClF, 3-Methylhexane, 3-Methylheptane, and 3-Methyloctane reveals that the calculated ORD is highly sensitive to basis functions even if they do not significantly contribute to the energy. The effect may be so pronounced that it changes the sign of the ORD, which is decisive for determining absolute configurations experimentally. p-type basis functions are even more sensitive, which may be expected due to their increased polarizability and directionality. We seem to have found a distance dependence of the extrema of the computed ORD and the radial part of the basis functions used on the stereogenic center.

Hence, with such a correlation we propose to devise a rule for choosing a good basis to compute ORDs based on geometry of the molecule.

Abstract Author(s): B. Christopher Rinderspacher, Peter R. Schreiner