The (-) enantiomer of a compound has a specific rotation of [a] = 86o. A sample of this pure enantiomer, when measured in the polarimeter in a two dm sample tube, gives an observed rotation of a = -4.3o. What is the concentration of this sample in g/mL?



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[a] = a/(c x l)

 


The specific rotation, [a] = 86o

The observed rotation, a = -4.3o

The length of the analysis tube is two dm;  l = 2.0 dm





















































Solution:

The specific rotation, [a] = 86o

The observed rotation, a = -4.3o

The length of the analysis tube is two dm;  l = 2.0 dm



The concentration is therefore:


[a] = 86o = -4.3o/(c  x 2.0 dm)


 c = 0.025 g/mL


 

























































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