These values should always be accompanied by information about the temperature, solvent and wavelength of light used, as all of these variables can affect the specific rotation. dm −1, which are typically shortened to just degrees, wherein the other components of the unit are tacitly assumed.Values for specific rotation are reported in units of deg Here θ is the Celsius temperature and λ the wavelength of the light at which the measurement is carried out. The CRC Handbook of Chemistry and Physics defines specific rotation as:įor an optically active substance, defined by θ λ = α/γl, where α is the angle through which plane polarized light is rotated by a solution of mass concentration γ and path length l. : 124 The concentration of bulk sugar solutions is sometimes determined by comparison of the observed optical rotation with the known specific rotation. The variance of specific rotation with wavelength-a phenomenon known as optical rotatory dispersion-can be used to find the absolute configuration of a molecule. As such, the observed rotation ( α) of a sample of a compound can be used to quantify the enantiomeric excess of that compound, provided that the specific rotation ( ) for the enantiopure compound is known. Specific rotation is an intensive property, distinguishing it from the more general phenomenon of optical rotation. : 245 If a compound is able to rotate the plane of polarization of plane-polarized light, it is said to be “ optically active”. : 2–65 Compounds which rotate the plane of polarization of a beam of plane polarized light clockwise are said to be dextrorotary, and correspond with positive specific rotation values, while compounds which rotate the plane of polarization of plane polarized light counterclockwise are said to be levorotary, and correspond with negative values. : 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. In chemistry, specific rotation ( ) is a property of a chiral chemical compound. This angle is determined with a rotatable polarizing filter (7). Recording optical rotation with a polarimeter: The plane of polarisation of plane polarised light (4) rotates (6) as it passes through an optically active sample (5).
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