A solution containing 0.08 g/mL of a pure R enantiomer in a 1 dm polarimeter rotates plane polarized light by +4°.What is the specific rotation of the S enantiomer?
A)+50°
B)-40°
C)+40°
D)-50°

Question

Quizplus · Accepted Answer

Since the R enantiomer rotates plane polarized light by +4°, we can use the specific rotation formula:

specific rotation = observed rotation / (concentration x path length)

We know the concentration is 0.08 g/mL and the path length is 1 dm (which is 10 cm or 0.1 m). Therefore,

specific rotation (R) = +4° / (0.08 g/mL x 0.1 m) = +50° (note: we convert dm to m)

Since the S enantiomer is the mirror image of the R enantiomer, it will rotate the plane polarized light in the opposite direction. Therefore, the specific rotation of the S enantiomer is:

specific rotation (S) = -50°

Thus, the correct answer is D.

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