Specific rotation

In chemistry, specific rotation ([α]) is a property of a chiral chemical compound. It is defined as the change in orientation of monochromatic plane-polarized light, per unit distance–concentration product, as the light passes through a sample of a compound in solution. Compounds which rotate light clockwise are said to be dextrorotary, and correspond with positive specific rotation values, while compounds which rotate light counterclockwise are said to be levorotary, and correspond with negative values. If a compound is able to rotate plane-polarized light, it is said to be “optically active”.