Optical rotation

Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of <a href="/facts/Polarization_(waves)/fP33m0eD">polarization</a> about the optical axis of <a href="/facts/Linear_polarization/y4nJQKS1">linearly polarized</a> light as it travels through certain materials. Circular birefringence and <a href="/facts/Circular_dichroism/sMKgzpF2">circular dichroism</a> are the manifestations of optical activity. Optical activity occurs only in <a href="/facts/Chiral/hjx0eGrB">chiral</a> materials, those lacking microscopic mirror symmetry. Unlike other sources of <a href="/facts/Birefringence/J4lLuR3a">birefringence</a> which alter a beam's state of polarization, optical activity can be observed in <a href="/facts/Fluid/tMQ46Tmz">fluids</a>. This can include gases or solutions of <a href="/facts/Chirality_(chemistry)/p5a9pftB">chiral molecules</a> such as sugars, molecules with helical <a href="/facts/Secondary_structure/VaN6MEYh">secondary structure</a> such as some proteins, and also <a href="/facts/Liquid_crystal/ehCCST89">chiral liquid crystals</a>. It can also be observed in chiral solids such as certain crystals with a rotation between adjacent <a href="/facts/Crystal/e2R2mk3E">crystal</a> planes (such as <a href="/facts/Quartz/4n86tE2G">quartz</a>) or <a href="/facts/Metamaterial/3DeLU6ME">metamaterials</a>.
When looking at the source of light, the rotation of the plane of polarization may be either to the right (dextrorotatory or dextrorotary — d-rotary, represented by (+), clockwise), or to the left (levorotatory or levorotary — l-rotary, represented by (−), counter-clockwise) depending on which <a href="/facts/Stereoisomer/I3kzlDE8">stereoisomer</a> is dominant. For instance, <a href="/facts/Sucrose/7y1ke94L">sucrose</a> and <a href="/facts/Camphor/53KvP2Rw">camphor</a> are d-rotary whereas <a href="/facts/Cholesterol/TnfPlYc1">cholesterol</a> is l-rotary. For a given substance, the angle by which the polarization of light of a specified wavelength is rotated is proportional to the path length through the material and (for a solution) proportional to its concentration.
Optical activity is measured using a polarized source and <a href="/facts/Polarimeter/7HnQDxQC">polarimeter</a>. This is a tool particularly used in the <a href="/facts/Sugar_industry/rvRmVQk4">sugar industry</a> to measure the sugar concentration of syrup, and generally in chemistry to measure the concentration or <a href="/facts/Enantiomer/wjPv5J3y">enantiomeric ratio</a> of chiral molecules in solution. Modulation of a liquid crystal's optical activity, viewed between two sheet <a href="/facts/Polarizer/kPDwyboP">polarizers</a>, is the principle of operation of <a href="/facts/Liquid-crystal_display/8B6xGBEz">liquid-crystal displays</a> (used in most modern televisions and computer monitors).

Optical rotation open-in-new

Optical rotation