Understanding Vibrational Circular Dichroism
Many molecules in our world, and especially in our biological systems, are chiral.
Chiral molecules cannot be superimposed on their mirror image, and especially when no similar compound exists that can act as a reference, it can be immensely difficult to know which of the two enantiomers present in a sample is the original.
Since the 1960s, circular dichroism (which is the difference in how left and right circularly polarised light is absorbed in a sample) has been used to determine the handedness of tris-chelate metal complexes, steroids, and other molecules which are very small.
However, circular dichroism is not universal. Available electronic transitions and awareness of the mechanism that leads to the observed signal are necessary in circular dichroism.
Conversely, vibrational circular dichroism (VCD) is potentially a universal technique. Because all molecules have vibrations and helical shapes are produced through the vibrations of chiral molecules, calculation of the VCD spectrum is possible for almost all small molecules.