Chiroptical methods polarimetry

The basic instrumental needs for chiroptical methods are virtually the same as for other spectroscopic methods, namely, a stable unpolarized illuminating source of sufficient intensity, a wavelength-selection device, sample holder, and detector polarizing elements are essential. Because the only parameter measured in polarimetry and ORD is rotation, the polarizing elements are common to both. A monochromatic source, such as an Na or Hg lamp, is all that is required for polarimetry. Deuterium or halogen lamps are of sufficient intensity for ORD, but highly intense (150 50 W) Xe arc lamps are needed for CD. 

The interaction of polarized light with chiral compounds is of great interest since chiroptical techniques are extremely useful as methods of characterization. It is equally true that although most scientists are aware that enantiomerically rich solutions will rotate the plane of linearly polarized light, the origins of this effect are not as simple as might be imagined. In this first article, the phenomena of polarimetry and optical rotatory dispersion will be discussed. A subsequent note will concern the related phenomenon of circular dichroism. 

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