During the course of your career as a natural products chemist you isolate a new

Question

During the course of your career as a natural products chemist you isolate a new compound from a plant in South America that has excellent cytotoxic activity against tumor cells. Because you have isolated the compound as a pure enantiomer, you wish to report its optical activity. A 0.500-g sample of the compound is placed in 10 mL of ethanol in a sample tube and placed in the polar meter. The observed optical rotation (alpha) is measured to be +0.530 degrees. If the length of the sample tube (l) is 10.0 cm, what is the calculated value for the specific rotation ([alpha]) of this new compound? A. (+) 1.06 B. (+) 10.6 C. (+) 100.6 D. (+) 0.106 E. (+) 0.53

Explanation / Answer

Given optical rotation : +0.530 degree

Length of the tube = 10 cm = 1 dm (decimeter)

Concentration = 0.5 g in 10 mL = 0.5 g in 10 cm3 = 0.05 g in 1 cm3   (1 mL = 1 cm3)

Specific rotation = (optical rotation)/(C x l)

Where C = concentration of the sample in 1 cm3

and l = lenth of tube in dm

Specific rotation = (optical rotation)/C x l = +0.53/(0.05 x 1) = (+)10.6

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