VIBRATIONAL ABSORPTION AND CIRCULAR-DICHROISM OF MONOMETHYL AND DIMETHYL DERIVATIVES OF 6,8-DIOXABICYCLO[3.2.1]OCTANE

Ab initio density functional theory (DFT) is used to analyze the vibra tional unpolarized absorption and circular dichroism spectra (below 15 00 cm(-1)) of seven derivatives of 6,8-dioxabicyclo[3.2.1]octane. Two are methyl derivatives, two are methyl-d(3) derivatives, and three are dimethyl derivatives. DFT calculations use hybrid functionals (B3LYP and B3PW91), the 6-31G basis set, and, in predicting circular dichroi sm spectra, GIAO basis sets. The two functionals give qualitatively si milar spectra. Comparison of predicted and experimental spectra permit s assignment of the majority of the fundamentals of the seven molecule s (excluding C-H stretching modes). Vibrational circular dichroism int ensities are in good overall agreement with experiment, consistent wit h previously assigned absolute configurations. Spectra are also predic ted using the Hartree-Fock/self-consistent field (HF/SCF) and MP2 meth odologies. MP2 spectra are similar in accuracy to DFT spectra. HF/SCF spectra are of much lower accuracy and are in poor agreement with expe riment.