Optical activity

Optical Activity is a property of certain chemical substances and crystals that allows them to rotate the plane of polarized light. This phenomenon is observed in substances that lack an internal plane of symmetry, known as chiral substances.

Overview

Optical activity is a form of birefringence, where the refractive index of a substance varies depending on the polarization and propagation direction of light. The rotation of the plane of polarization is usually specified in degrees (°) for a given path length and light wavelength.

Chirality and Optical Activity

Chirality is a property of an object which is not superposable on its mirror image. In chemistry, it usually refers to molecules. Chiral molecules with one chiral center can exist in two forms, or enantiomers, which are mirror images of each other.

Many chiral substances can rotate the plane of polarized light. The direction of this rotation determines whether the substance is termed dextrorotatory (rotation to the right, or clockwise) or levorotatory (rotation to the left, or counterclockwise).

Measurement of Optical Activity

The measurement of optical activity is performed using a polarimeter. The observed rotation is reported as the specific rotation, which is the rotation in degrees per decimeter of path length per gram per milliliter of sample concentration.

Applications

Optical activity is used in many areas of science and technology, including chemistry, biochemistry, pharmaceutical industry, and material science. It is particularly important in the study and synthesis of pharmaceuticals, as the different enantiomers of a chiral drug can have different biological effects.

See Also

• Polarized light
• Chirality (chemistry)
• Enantiomer
• Polarimeter