Optical rotation

optically activeoptical activityoptically inactiveCircular birefringencechiralcircularly birefringentnatural optical activityoptical angle of rotationoptically stablepolarization direction
Optical rotation or optical activity (sometimes referred to as rotary polarization) is the rotation of the plane of polarization of linearly polarized light as it travels through certain materials.wikipedia
168 Related Articles

Polarization (waves)

polarizationpolarizedpolarized light
Optical rotation or optical activity (sometimes referred to as rotary polarization) is the rotation of the plane of polarization of linearly polarized light as it travels through certain materials.
The most common optical materials (such as glass) are isotropic and do not affect the polarization of light passing through them; however, some materials—those that exhibit birefringence, dichroism, or optical activity—can change the polarization of light.

Birefringence

birefringentdouble refractionbiaxial
Unlike other sources of birefringence which alter a beam's state of polarization, optical activity can be observed in fluids. Whereas linear birefringence in a crystal involves a small difference in the phase velocity of light of two different linear polarizations, circular birefringence implies a small difference in the velocities between right and left-handed circular polarizations. Think of one enantiomer in a solution as a large number of little helices (or screws), all right-handed, but in random orientations.
Circular birefringence in liquids where there is an enantiomeric excess in a solution containing a molecule which has stereo isomers.

Polarimeter

Photopolarimeterconcentration of bulk sugar solutionsImaging polarimeter
Optical activity is measured using a polarized source and polarimeter.
A polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance.

Faraday effect

FaradayFaraday Rotationrotation measure
Rotation of light's plane of polarization may also occur through the Faraday effect which involves a static magnetic field, however this is a distinct phenomenon that is not usually classified under "optical activity."
The Faraday effect is caused by left and right circularly polarized waves propagating at slightly different speeds, a property known as circular birefringence.

Stereoisomerism

stereoisomerstereoisomers(''E'') and (''Z'')
The rotation of the plane of polarization may be either clockwise, to the right (dextrorotary — d-rotary), or to the left (levorotary — l-rotary) depending on which stereoisomer is present (or dominant).
Pure enantiomers also exhibit the phenomenon of optical activity and can be separated only with the use of a chiral agent.

Chirality (chemistry)

chiralchiralityoptical isomer
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.
The term optical activity is derived from the interaction of chiral materials with polarized light.

Inverted sugar syrup

invert sugarinverted sugaran inverted syrup
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.
This mixture has the opposite direction of optical rotation as the original sugar, which is why it is called an invert sugar.

Louis Pasteur

PasteurPasteur, LouisPasteurian
In 1849, Louis Pasteur resolved a problem concerning the nature of tartaric acid.
A solution of this compound derived from living things rotated the plane of polarization of light passing through it. The problem was that tartaric acid derived by chemical synthesis had no such effect, even though its chemical reactions were identical and its elemental composition was the same.

François Arago

AragoDominique-François-Jean AragoDominique François Jean Arago
The rotation of the orientation of linearly polarized light was first observed in 1811 in quartz by French physicist François Jean Dominique Arago.
The subsequent invention of the polariscope and discovery of Rotary polarization are due to Arago.

Racemic mixture

racemicracemateracemates
If two enantiomers are present in equal proportions then their effects cancel out and no optical activity is observed; this is termed a racemic mixture.
A racemate is optically inactive, meaning that there is no net rotation of plane-polarized light.

Jacobus Henricus van 't Hoff

van 't Hoffvan't HoffJacobus van 't Hoff
In 1874, Jacobus Henricus van 't Hoff and Joseph Achille Le Bel independently proposed that this phenomenon of optical activity in carbon compounds could be explained by assuming that the 4 saturated chemical bonds between carbon atoms and their neighbors are directed towards the corners of a regular tetrahedron.
In 1874, he accounted for the phenomenon of optical activity by assuming that the chemical bonds between carbon atoms and their neighbors were directed towards the corners of a regular tetrahedron.

Polarizer

polarizing filtercircular polarizerpolarized
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).
This effect is used in polarimetry to measure the optical activity of a sample.

Plane of polarization

Rotation of light's plane of polarization may also occur through the Faraday effect which involves a static magnetic field, however this is a distinct phenomenon that is not usually classified under "optical activity."
In an optically chiral medium — that is, one in which the "plane of polarization" gradually rotates as the wave propagates — the choice of definition does not affect the existence or direction ("handedness") of the rotation.

Optical rotatory dispersion

optical rotationoptical rotatory power
The resulting variation in rotation with the wavelength of the light is called optical rotatory dispersion (ORD).
Optical rotatory dispersion is the variation in the optical rotation of a substance with a change in the wavelength of light.

Circular dichroism

CDcircular dichroism spectroscopyhelicity
ORD spectra and circular dichroism spectra are related through the Kramers–Kronig relations.
It is exhibited in the absorption bands of optically active chiral molecules.

Jean-Baptiste Biot

BiotBiot, Jean BaptisteBiot, Jean-Baptiste
Jean Baptiste Biot also observed the rotation of the axis of polarization in certain liquids and vapors of organic substances such as turpentine.
His work in chromatic polarization and rotary polarization greatly advanced the field of optics, although it was later shown that his findings could also be obtained using the wave theory of light (Frankel 2009).

Organic chemistry

organicorganic chemistorganic chemical
Chiral molecules produced within the fields of organic chemistry or inorganic chemistry are racemic unless a chiral reagent was employed in the same reaction.
Traditional spectroscopic methods such as infrared spectroscopy, optical rotation, and UV/VIS spectroscopy provide relatively nonspecific structural information but remain in use for specific classes of compounds.

Circular polarization

circularly polarizedcircularly polarized lightcircular
Whereas linear birefringence in a crystal involves a small difference in the phase velocity of light of two different linear polarizations, circular birefringence implies a small difference in the velocities between right and left-handed circular polarizations. Think of one enantiomer in a solution as a large number of little helices (or screws), all right-handed, but in random orientations.
In general, this phenomenon will be exhibited in absorption bands of any optically active molecule.

Specific rotation

So we find that the degree of rotation depends on the color of the light (the yellow sodium D line near 589 nm wavelength is commonly used for measurements), and is directly proportional to the path length L through the substance and the amount of circular birefringence of the material \Delta n which, for a solution, may be computed from the substance's specific rotation and its concentration in solution.
If a compound is able to rotate the plane of polarization of plane-polarized light, it is said to be “optically active”.

Enantiomeric excess

eeoptical puritydiastereomeric excess
But when there is an enantiomeric excess, more of one enantiomer than the other, the cancellation is incomplete and optical activity is observed.
A non-racemic mixture of two enantiomers will have a net optical rotation.

Dextrorotation and levorotation

dextrorotatorylevorotatorydextrorotary
The rotation of the plane of polarization may be either clockwise, to the right (dextrorotary — d-rotary), or to the left (levorotary — l-rotary) depending on which stereoisomer is present (or dominant).
Compounds with these properties are said to have optical activity and consist of chiral molecules.

Polarimetry

polarimetricpolariscopespectropolarimetry
This usage makes a polarimeter a tool of great importance to those trading in or using sugar syrups in bulk.
Polarimetry can be used to measure various optical properties of a material, including linear birefringence, circular birefringence (also known as optical rotation or optical rotary dispersion), linear dichroism, circular dichroism and scattering.

Optic axis of a crystal

optic axisoptic axesbiaxial positive
Although quartz has a substantial linear birefringence, that effect is cancelled when propagation is along the optic axis.
For light propagating along an optic axis, though, the speed does not depend on the polarization, so there is no birefringence although there can be optical activity (a rotation of the plane of polarization).