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A compound has a specific rotation of -39.0. A solution of
Chapter 4, Problem 75P(choose chapter or problem)
Problem 75P
A compound has a specific rotation of -39.0. A solution of the compound (0.187 g/100 mL) has an observed rotation of -6.52o when placed in a polarimeter tube 10 cm long. What is the percent of each enantiomer in the solution?
Questions & Answers
QUESTION:
Problem 75P
A compound has a specific rotation of -39.0. A solution of the compound (0.187 g/100 mL) has an observed rotation of -6.52o when placed in a polarimeter tube 10 cm long. What is the percent of each enantiomer in the solution?
ANSWER:
Solution:
Here we have to calculate the percent of each enantiomer present in the solution.
Enantiomers: - When a pair of molecules are a mirror image of each other is said to be enantiomers and form complementary structure i.e one compound is R and the other is S.
Specific rotation: - It is a property of chiral compound and is defined as the change in orientation of the monochromatic plane polarized light per unit distance.
Step 1
Given:
The specific rotation of an unknown compound is -39.0
Concentration = 0.187 g/100mL
Observed rotation = -6.52o
Width of polarimeter tube (length) = 10 cm = 1dm
It is known that the expression for observed specific rotation can be written as,
Observed specific rotation =
Now substituting the values ,
= = -34.9o
Thus the observed specific rotation is found to be -34.9o.