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Optical activity


Synonyms: Optical rotation, optical rotatory power

Optical activity is the ability of a compound to rotate the plane polarized light. The specific rotation is quantitatively expressed as:

Formula for specific optical rotation

Where the observed rotation is in degrees times 100, the length of the optical path is dm (decimeter = 10 cm) and the concentration in g/100 mL. The temperature is usually 25oC and the wavelength where the rotation is measured is the D-line of sodium at 589.3 nm. The cuvettes used in polarometers is usually 10cm in length. The specific rotation of a compound e.g. an amino acid depends on the temperature and the pH of the solution. The specific rotation is measured in degrees.

Compounds which rotate the plane of polarized light to the right is called dextrorotatory and is designated with the symbol (+). Compounds which rotate the plane to the left is called levorotatory and is designeted with (-). In the older literature the designations are D and L respectively.

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