Knowledge Bank

Vibrational circular dichroism (VCD) in tartaric acid, dimethyl tartrate, diethyl tartrate and diisopropyl tartrate have been measured in $CCl4$ and DMSO solvents. These measurements, which arc in addition to those reported $earlier,1$ inidicate that the VCD associated with $C\ast -O$ stretching vibrations is identical in all the molecules of the present series. However, VCD associated with the $C=O$ stretching vibration differs from molecule to molecule. These differences are attributed to the well known internal hydrogen bonding and the influence there on from the substituents in COOR group. In order to get a physical picture of the different possible hydrogen bonded conformers, ab initio calculations have been carried out and the minimum energy conformers are identified. The conclusions emerging from these studies point to the extreme sensitivity of VCD, associated with the $C=O$ stretching vibrations, to the nature of internal hydrogen bonding.