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Specific rotation is a property of a chiral chemical compound. 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. Specific rotation of a compound is a characteristic property of the compound as long as the temperature, the wavelength of the light, and the solvent are specified.
Measurement of Specific Rotation
Following are formulas used for calculation of specific rotation:
- α-the measured rotation in degrees
- t - the temperature
- λ- the wavelength of light
- l - the length in decimeters of the light path through the solution
- c - the concentration in grams of sample per 100 ml of solution
- d - the density of liquid in grams/ml
Optical rotation (measured rotation) is measured with an instrument called a polarimeter. Polarimeter is the instrument that measures the direction and angles of rotation of plane-polarized light. The plane-polarized light pass through the sample tube containing the solution of sample, and the angle of rotations will be received and recorded by the analyzer, as summarized in Fig.1. And the observed rotation depends on the length of the sample tube, concentration of the sample and temperature.
Fig. 1 Measurement of Optical Rotation with Polarimeter
There is a linear relationship between the observed rotation and the concentration of optically active compound in the sample. There is a non-linear relationship between the observed rotation and the wavelength of light used. Specific rotation is calculated using either of two equations above.
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Chemists from Alfa Chemistry have a great deal of experience in the tests of chemicals. Our experienced chemists are pleased to work with you to solve your problems in scientific research and industrial applications. Alfa Chemistry offers specific rotation tests of various chemicals. Please feel free to contact us for more details.