Specific rotation

The specific rotation of a chemical compound D is defined as the observed optical rotation (a) when light of 598 nanometer wavelength is passed through a sample with a sample path (l) of 0.1 meter and a sample concentration (C) of 1 gram per milliliter.

Related Topics:
Chemical compound - Optical rotation - Nanometer - Wavelength

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:_D^T = rac{a}{l * C}

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When the specific rotation is larger than 360° the sample gets diluted. The correct notation is deg cm2 g-1 but in the literature it is just degrees. The value is always accompanied by the temperature at which the measurement is carried out. The solvent is normally water so if another solvent is used that too should be stated.

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If the rotation is levorotatory a minus sign is added to the value and with dextrorotatory rotation the sign is plus. Specific rotation is measured in a device called a polarimeter. The specific rotation is a physical property of an optically active compound. Some examples:

Related Topics:
Levorotatory - Dextrorotatory - Polarimeter - Optically active compound

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• Sucrose +66.47°
• cholesterol −31.5°
• Camphor +44.26°
• Penicillin V +223°
• taxol −49°
• (S)-bromobutane +23.1°
• (R)-bromobutane −23.1°
• (+)-cavicularin +168.2°

Specific rotation provides a way to assess optical purity of a sample. For example when in a sample of bromobutane the specific rotation is −9.2° the enantiomeric excess of the R enantiomer is (100%}(9.2°/23.1°) or 40%. The remaining 60% of the sample is racemic (30% R and 30% S) and therefore the total concentration of R is 70%.

Related Topics:
Enantiomeric excess - Enantiomer - Racemic

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