Density functional theory calculations of vibrational absorption and circular dichroism spectra of dimethyl-l-tartrate

Vibrational absorption and circular dichroism (VCD) spectra of dimethyl-L-tartrate have been measured in CCl4 solution in the mid-infrared spectral range. Experimental spectra have been compared with the density functional theory (DFT) absorption and VCD spectra calculated using the B3LYP functional and 6-31G* basis set for nine conformers of dimethyl-L-tartrate. The minimum-energy structure of each conformer has been calculated without constraining the molecule to be of C-2 symmetry. These calculations indicate that the trans COOR conformation with hydrogen bonding between the OH and C=O groups attached to the same chiral carbon is of lowest energy and represents more than 83% of the different conformers at room temperature. The vibrational absorption and circular dichroism calculated from this conformation are in very good overall agreement with experiment. Finally, the limitation of the coupled oscillator model has been shown to interpret the VCD response in the OH stretching region.