optical activity

from The American Heritage® Dictionary of the English Language, 4th Edition

• n. Chemistry A property caused by asymmetrical molecular structure that enables a substance to rotate the plane of incident polarized light.

from Wiktionary, Creative Commons Attribution/Share-Alike License

• n. a property caused by asymmetrical molecular or crystal structure that enables a compound or crystal to rotate the plane of incident polarized light
• n. A measure of the amount of optical rotation produced by a standard amount of a substance

from the GNU version of the Collaborative International Dictionary of English

• n. the ability of a chemical compound to rotate the plane of plane-polarized light. This is found only in chemicals whose molecular structure does not have a plane of symmetry, and is common in biochemical compounds.