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Specific Rotation

  • Page ID
    42853
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    Observed rotation of an optically active compound, measured using the polarimeter, depends on the experimental conditions and, therefore, is not a characteristic property of the compound. Specific rotation (symbol: [α]λT) of an optically active compound is defined as follows:

    specificrotation1.png

    α = observed rotation measured using a polarimeter
    l = length of sample tube
    C = concentration, if a solution of the compound is used for the experiment, or density, if a neat sample of the compound is used
    T = Temperature (usually 25 ºC)
    λ = wave length of the light used (usually 589 nm)

    Specific rotation of a compound is a characteristic property of the compound as long as the temperature, the wave length of the light, and, if a solution is used for the experiment, the solvent are specified. The units of specific rotation are degreesmLg-1dm-1. However, since the units of specific rotation are always the above, traditionally, specific rotation is reported without units.

    eg:

    specificrotation2.png


    This page titled Specific Rotation is shared under a All Rights Reserved (used with permission) license and was authored, remixed, and/or curated by Gamini Gunawardena via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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