What is Optical activity: Definition and 12 Discussions

Optical rotation, also known as polarization rotation or circular birefringence, is the rotation of the orientation of the plane of polarization about the optical axis of linearly polarized light as it travels through certain materials. Circular birefringence and circular dichroism are the manifestations of optical activity. Optical activity occurs only in chiral materials, those lacking microscopic mirror symmetry. Unlike other sources of birefringence which alter a beam's state of polarization, optical activity can be observed in fluids. This can include gases or solutions of chiral molecules such as sugars, molecules with helical secondary structure such as some proteins, and also chiral liquid crystals. It can also be observed in chiral solids such as certain crystals with a rotation between adjacent crystal planes (such as quartz) or metamaterials.
The rotation of the plane of polarization may be either clockwise, to the right (dextrorotary — d-rotary, represented by (+), or to the left (levorotary — l-rotary, represented by (-) depending on which stereoisomer is present (or dominant). For instance, sucrose and camphor are d-rotary whereas cholesterol 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 polarimeter. This is a tool particularly used in the sugar industry to measure the sugar concentration of syrup, and generally in chemistry to measure the concentration or enantiomeric ratio of chiral molecules in solution. Modulation of a liquid crystal's optical activity, viewed between two sheet polarizers, is the principle of operation of liquid-crystal displays (used in most modern televisions and computer monitors).

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  1. Dyn Doeth

    A Structural coloration of a zeolite monolayer

    I have a monolayer of zeolite crystals on glass with the thickness of the zeolites about 800nm. When I look at the reflection of fluorescent light bulbs on this monolayer, the reflection is white except at specific angles. At around 45 deg, the colour appears red/magenta and at a lower angle...
  2. M

    Tensor Inverse (Optical Activity)

    Clearly, they used the binomial expansion on this; however, I cannot figure out why [G] is sandwiched by the epsilon inverses: $$\varepsilon^{'-1}=1/(\varepsilon+i\epsilon_{0}[G])\approx(1-i\epsilon_{0}[G]\varepsilon^{-1})\varepsilon^{-1}$$
  3. P

    Chemistry Structural formulas & optical activity

    How do I determine which group is dash (into the page) and which is wedge (out of page)? Won't that literally change which isomer it is? How to determine optical activity then? (I believe that in order for something to be optically active it has to be an enantiomer--a non-superimposable mirror...
  4. Paul Colby

    Can Crystal Symmetry Explain the Lack of Optical Activity in Quartz?

    Hi, I've been looking at the optics of ##\alpha##-quartz which comes in two parities, left and right. Quartz is optically active which means that the plane of a linearly polarized beam propagating along the optic axis is rotated by an angle proportional to the distance traveled. I would like...
  5. Wrichik Basu

    Reason for Optical Isomerism (at electron level)

    I have been studying Optical Isomerism recently, and I have got one question, answer to which was not in the books that I have. I have understood what the phenomenon is, and that, how one can determine whether the plane of polarised light is rotated, and how to tell from the structure whether...
  6. R

    Refractive index as a function of the concentration of a sugar solution

    We recently performed an experiment with the idea to find refractive index of medium (water) as a function of wavelength of light. We then added some sugar to see how the refractive index changes with concentration of sugar solution. We got the following graphs. Are the relationships actually...
  7. Incnis Mrsi

    A Chirality of the electromagnetic force on atomic matter

    It’s commonly held that left and right photons interact with matter in exactly the same way, because electromagnetism “conserves parity”. But we know that P-symmetry, in our world, is generally broken. Even according to the Standard Model, when light propagates through some media, it interacts...
  8. T

    Difference between optically active and inactive compounds

    Any polarised light's plane is shifted while passing from one medium to another for refraction. So, optically active or not, a solution of any compound will cause refraction because of its density. Then what's special in an optically active compound?
  9. V

    Optical Activity: How Do Chiral Molecules Rotate Light?

    "Optical activity is the tendency of chiral molecules to rotate ppl" how does a chiral molecule rotate light? Is it because of interaction of electric fields? Anyone please help me? I just need to know how a molecule physically does that?
  10. C

    How Does Optical Activity Help Measure Sugar Concentration?

    Homework Statement The sugar concentration in a solution (e.g., in a urine specimen) can be measured conveniently by using the optical activity of sugar and other asymmetric molecules. In general, an optically active molecule, like sugar, will rotate the plane of polarization through an angle...
  11. K

    How Does Optical Activity Help Measure Sugar Concentration?

    The sugar concentration in a solution can be measured conveniently by using the optical activity of sugar nad other asymmetric molecules. In general, an optically active molecule like sugar will rotate the plane of polarization through an angle that is proportional to the thickness of the sample...
  12. A

    Optical Activity: How Do Organic Substances Rotate Polarized Light?

    optically active organic substances have the ability to rotate the plane of polarization of plane-polarized light. what i want to know is that how exactly do they rotate it?