Specific Rotation of Chiral Molecules

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SUMMARY

The specific rotation of (R)-(+)-limonene can be lower than the literature value due to the presence of achiral solvents such as methylene chloride, which can dilute the optical activity of the chiral compound. The discussion emphasizes that while ethanol is used as a solvent, the inclusion of methylene chloride can still impact the specific rotation measurement. To accurately calculate specific rotation, one must consider the observed angle of rotation and the concentration of the sample in the polarimeter.

PREREQUISITES
  • Understanding of specific rotation and its calculation.
  • Familiarity with polarimetry and how it measures optical activity.
  • Knowledge of chiral and achiral molecules.
  • Basic principles of solvent effects on optical properties.
NEXT STEPS
  • Research the calculation methods for specific rotation in chiral compounds.
  • Learn about the effects of different solvents on optical activity in organic chemistry.
  • Study the principles of polarimetry and its applications in measuring chiral substances.
  • Investigate the role of enantiomers in optical rotation and their impact on specific rotation values.
USEFUL FOR

Chemistry students, organic chemists, and researchers involved in stereochemistry and the analysis of chiral molecules will benefit from this discussion.

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Homework Statement


Why may the specific rotation of a sample of (R)-(+)-limonene be less than the literature value of (R)-(+)-limonene. Assume that there are so (S) enantiomers present.


Homework Equations





The Attempt at a Solution


There are no (S) enantiomers, but there are some molecules of methylene chloride mixed into the sample that was analyzed. But since these are achiral, I don't understand why they should affect the rotation of the limonene.
 
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When you calculate the specific rotation of a sample, what values do you need to know? Would the presence of solvent affect any of those values?
 
Ygggdrasil said:
When you calculate the specific rotation of a sample, what values do you need to know? Would the presence of solvent affect any of those values?

The solvent used was ethanol, so that should not affect the optical activity. Are there any other factors which would affect it? Like the presence of methylene chloride perhaps? And why would it affect it?
 
Again, think about how you calculate the specific rotation of a sample. You place your sample in the polarimerter and obtain the angle by which your sample rotated the light. How do you calculate the specific rotation from that value?
 

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