OPTICAL ROTATION: Substances that may show optical rotatory power are chiral. Those that rotate light in a clockwise direction as viewed towards the light source are dextrorotatory, or (+) optical isomers. Those that rotate light in the opposite direction are called levorotatory or (–) optical isomers. SPECIFIC ROTATION : The specific rotation of a chemical compound [α] is defined as the observed angle of optical rotation α, when plane-polarized light is passed through a sample with a path length of 1 decimeter and a sample concentration of 1 gram per 1 deciliter. The specific rotation of a pure material is an intrinsic property of that material at a given wavelength and temperature. General Testing Procedure , OPTICAL , ROTATION