 optical rotation (optical activity) is the turning of the plane of linearly polarized light about the direction of motion as the light travels through certain materials. it occurs in solutions of chiral molecules such as sucrose (sugar), solids with rotated crystal planes such as quartz, and spin-polarized gases of atoms or molecules. it is used in the sugar industry to measure syrup concentration, in optics to manipulate polarization, in chemistry to characterize substances in solution, and in optical mineralogy to help identify certain minerals in thin sections. it is being developed as a method to measure blood sugar concentration in diabetic people. == history ==  the rotation of the orientation of linearly polarized light was first observed in 1811 in quartz by french physicist franÃ§ois jean dominique arago. in 1822, the english astronomer sir john f.w. herschel discovered that different individual quartz crystals, whose crystalline structures are mirror images of each other (see illustration), rotate linear polarization by equal amounts but in opposite directions. jean baptiste biot also observed the rotation of the axis of polarization in certain liquids and gases of organic substances such as turpentine. simple polarimeters have been used since this time to measure the concentrations of simple sugars, such as glucose, in solution. in fact one name for d-glucose (the biological isomer), is dextrose, referring to the fact that it causes linearly polarized light to rotate to the right or dexter side. in a similar manner, levulose, more commonly known as fructose, causes the plane of polarization to rotate to the left. fructose is even more strongly levorotatory than glucose is dextrorotatory. invert sugar syrup, commercially formed by the hydrolysis of sucrose syrup to a mixture of the component simple sugars, fructose, and glucose, gets its name from the fact that the conversion causes the direction of rotation to "invert" from right to left. in 1849, louis pasteur resolved a problem concerning the nature of tartaric acid. a solution of this compound derived from living things (to be specific, wine lees) rotates the plane of polarization of light passing through it, but tartaric acid derived by chemical synthesis has no such effect, even though its reactions are identical and its elemental composition is the same. pasteur noticed that the crystals come in two asymmetric forms that are mirror images of one anothe
Polarization_(waves) Stereochemistry