Rotary polarization

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Rotary polarization is an optical phenomenon occurring in solutions or gasses of certain molecules and also in some crystals. The vibrational direction of linearly polarized light propagating through such a material is rotated. The amount of polarization rotation is proportional to the path length through the material. The rotation may be either clockwise, to the right (dextrorotary - d-rotary), or left (levorotary - l-rotary) depending on which stereoisomer is present. For instance, sucrose and camphor are d-rotary whereas cholesterol is l-rotary.

Rotary polarization occurs in molecules and crystals that have no crystallographic mirror planes or inversion centers. Such materials are enantiomorphous (the existence of two chemically identical molecular or crystal forms as mirror images of each other). Thus crystalline quartz SiO2 exhibits rotary polarization whereas the amorphous forms of silica such as fused quartz do not.

François Arago is credited with the discovery of rotary polarization of quartz in 1811.

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