Conformational studies utilizing asymmetric torsional frequencies

The utility of asymmetric torsional frequencies, obtained from low frequency infrared and/or Raman spectra of the gas phase, for conformational studies is presented. Vibrational spectroscopy may well be the most generally applicable method to be used in the study of the conformations of certain types of small molecules with few substituents because infrared and Raman spectra can be recorded in all phases, and variable temperature experiments can also be conducted. Additionally, gas phase band contours in both the infrared and Raman spectra, along with Raman depolarization data, provide considerable structural information and lend confidence to conclusions arrived at from vibrational studies. The theory and experimental difficulties involved in the determination of potential functions governing internal rotation is presented, and illustrated by a few examples.