Specific Rotation Calculator:
Enter the values of observed angle of rotation, a(deg), path length, l(dm)and concentration, y(g/mL) to determine the value of Specific Rotation, SR(deg.mL/dm.g).
Specific Rotation:
Specific rotation is a physical property used to quantify the optical activity of a chiral compound, which is a substance capable of rotating plane-polarized light. This property is especially important in stereochemistry and is used to identify and analyze enantiomers in organic chemistry.
As plane-polarized light travels through a solution with an optically active compound, its polarization direction is tilted—either clockwise (dextrorotatory, +) or counterclockwise (levorotatory, –)—based on the molecular structure of the substance.
The degree of this optical rotation is influenced by several factors, including the solution’s concentration, the path length of the sample container, the light’s wavelength (typically the sodium D-line at 589 nm), and the temperature at which the observation is made.
Specific rotation standardizes these variables, allowing scientists to compare optical activities of substances under controlled conditions. It is denoted by the symbol [α] and is expressed in degrees·mL/(dm·g) for solids or degrees·mL/(dm·mol) for molar rotation.
This property is critical in the pharmaceutical industry, food chemistry, and quality control labs to assess purity and identity of optically active substances.
Specific Rotation, SR(deg.mL/dm.g)in degrees times millilitres per gram per decimetreequals the observed angle of rotation, a(deg) in degrees divided by the product of the path length, l(dm) in decimetres and the concentration, y(g/mL)in grams per millilitre.
Specific Rotation, SR(deg.mL/dm.g)= a(deg)/ l(dm)* y(g/mL)
SR(deg.mL/dm.g)= specific rotation in degrees times millilitres per gram per decimetre, deg.mL/dm.g.
a(deg)= observed angle of rotation in degrees, deg.
l(dm)= path length in decimetre, dm.
y(g/mL) = concentrartion in grams per millilitres, g/mL.
Specific Rotation Calculation:
- A solution of an optically active compound shows an observed rotation (a) of +4.8°, the concentration of the solution (y) is 0.12 g/mL, and the path length (l) of the polarimeter tube is 1.0 dm. Calculate the specific rotation.
Given: a(deg)= +4.8°, l(dm)= 1.0dm, y(g/mL) = 0.12g/mL.
Specific Rotation, SR(deg.mL/dm.g)= a(deg)/ l(dm)* y(g/mL)
SR(deg.mL/dm.g)= 4.8 / 1.0 * 0.12
SR(deg.mL/dm.g)= 4.8 / 0.12
SR(deg.mL/dm.g)= 40deg.mL/dm.g.
- The specific rotation (SR) of a compound is +25°, the solution concentration (y) is 0.5 g/mL, and the path length (l) is 2 dm. Find the observed rotation.
Given: SR(deg.mL/dm.g)= 25deg.mL/dm.g, l(dm)= 2dm, y(g/mL) = 0.5g/mL.
Specific Rotation, SR(deg.mL/dm.g)= a(deg)/ l(dm)* y(g/mL)
a(deg)= SR(deg.mL/dm.g)* l(dm)* y(g/mL)
a(deg)= 25 * 2 * 0.5
a(deg)= +25°.