The (+) enantiomer of a compound has an observed optical rotation of 1.72o when measured in a one dm tube at a concentration of 0.3 g/15 mL. Calculate the specific rotation for this molecule.


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[a] = a/(c x l)

 


The observed rotation, a = 1.72o

The concentration of 0.3 g/15 mL is equivalent to 0.02 g/mL;   c = 0.02 g/mL

The length of the analysis tube is one dm;  l = 1.0 dm





















































Solution:

The observed rotation, a = 1.72o

The concentration of 0.3 g/15 mL is equivalent to 0.02 g/mL;   c = 0.02 g/mL

The length of the analysis tube is one dm;  l = 1.0 dm



The specific rotation is therefore:


[a] = 1.72o/(0.02 g/mL x 1.0 dm)

[a] = 86o g-1 mL-1 dm-1


 
























































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