Specific Optical Rotation

Calculate specific rotation [α] of an optically active compound using polarimeter data.

Observed rotation α (degrees)

Path length l (dm)

1 dm = 10 cm

Concentration c (g/100 mL)

Wavelength (optional, usually 589 nm)

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deg·mL/(g·dm)

[α] = α / (l × c)

where α = observed rotation, l = path length in dm, c = concentration in g/100 mL.

Specific rotation is temperature and wavelength dependent (usually quoted for 20°C and sodium D line).
For pure liquids, concentration is replaced by density (g/mL).
A positive value indicates dextrorotatory, negative indicates levorotatory.