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Dextrorotation and laevorotation (also spelled levorotation) [1] [2] in chemistry and physics are the optical rotation of plane-polarized light.From the point of view of the observer, dextrorotation refers to clockwise or right-handed rotation, and laevorotation refers to counterclockwise or left-handed rotation.
In chemistry, specific rotation ([α]) is a property of a chiral chemical compound. [1]: 244 It is defined as the change in orientation of monochromatic plane-polarized light, per unit distance–concentration product, as the light passes through a sample of a compound in solution.
For wavelengths that are absorbed by the optically active sample, the two circularly polarized components will be absorbed to differing extents. This unequal absorption is known as circular dichroism. Circular dichroism causes incident linearly polarized light to become elliptically polarized. The two phenomena are closely related, just as are ...
Polarized light with its electric field along the plane of incidence is thus denoted p-polarized, while light whose electric field is normal to the plane of incidence is called s-polarized. P-polarization is commonly referred to as transverse-magnetic (TM), and has also been termed pi-polarized or π-polarized, or tangential plane polarized.
The rotation of plane polarized light by chiral substances was first observed by Jean-Baptiste Biot in 1812, [25] and gained considerable importance in the sugar industry, analytical chemistry, and pharmaceuticals. Louis Pasteur deduced in 1848 that this phenomenon has a molecular basis.
The (+) or (−) symbol is used to specify a molecule's optical rotation — the direction in which the polarization of light rotates as it passes through a solution containing the molecule. [12] When a molecule is denoted dextrorotatory, it rotates the plane of polarized light clockwise and can also be denoted as (+). [11]
A racemate is optically inactive , meaning that such materials do not rotate the polarization of plane-polarized light. Although the two enantiomers rotate plane-polarized light in opposite directions, the rotations cancel each other out because they are present in equal amounts of negative (-) counterclockwise ( levorotatory ) and positive ...
As polarized light passes through a chiral molecule, the plane of polarization, when viewed along the axis toward the source, will be rotated clockwise (to the right) or anticlockwise (to the left). A right handed rotation is dextrorotary (d); that to the left is levorotary (l). The d- and l-isomers are the same compound but are called enantiomers.