Polarimeter

JoVE Science Education
Organic Chemistry II
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JoVE Science Education Organic Chemistry II
Polarimeter

97,948 Views

07:12 min
April 30, 2023

Genel Bakış

Source: Vy M. Dong and Diane Le, Department of Chemistry, University of California, Irvine, CA

This experiment will demonstrate the use of a polarimeter, which is an instrument used to determine the optical rotation of a sample. Optical rotation is the degree to which a sample will rotate polarized light. Optically active samples will rotate the plane of light clockwise (dextrorotatory), designated as d or (+), or counterclockwise (levorotatory), designated as l or (−).

İlkeler

Prosedür

1. Preparing the Polarimeter Turn on instrument and let it warm up for 10 min. Make sure instrument is set to "optical rotation" mode. Prepare a blank sample in the polarimeter cell (1.5 mL total sample volume, 1 dm in length) containing only CHCl3. Make sure there are no air bubbles present. Place the blank cell in the holder and press "zero." 2. Preparation of Analyte Sample Prepare a stock solution of 10-15 mg of the chiral analyte in 1.5 mL CHCl3. Note the exact amount of compound used. 3. Measuring Optical Rotation Fill the cell with 1.5 mL of the prepared stock solution containing the sample. Place the cell in the holder and press "measure." The machine readout will give the optical rotation value. Remember to record the temperature as well. 4. Calculation of Specific Rotation The specific rotation of a compound is defined by the following equation: where α is the optical rotation value given by the polarimeter, l is the cell pathlength in dm, and c is the concentration of the solution in g/mL.

Sonuçlar

Representative results for the measurement and calculation of specific rotation for Procedures 1-4. Procedure Step Reading on polarimeter 1.4 0.000 3.2 +0.563 4.1 [α]25D = +77° (c 0.73, CHCl3) …

Applications and Summary

In this experiment, we have demonstrated the principles behind the polarimeter and how to measure and calculate the specific rotation of an optically active compound.

The polarimeter is an important instrument in the fine-chemical and pharmaceutical industries to assess the identity, purity, and quality of a compound. It is specifically used for the measurement of optical rotation of chiral compounds, which can be used to distinguish the identity of two enantiomers by confirming whether it is…

DEŞİFRE METNİ

1. Preparing the Polarimeter Turn on instrument and let it warm up for 10 min. Make sure instrument is set to "optical rotation" mode. Prepare a blank sample in the polarimeter cell (1.5 mL total sample volume, 1 dm in length) containing only CHCl3. Make sure there are no air bubbles present. Place the blank cell in the holder and press "zero." 2. Preparation of Analyte Sample Prepare a stock solution of 10-15 mg of the chiral analyte in 1.5 mL CHCl3. Note the exact amount of compound used. 3. Measuring Optical Rotation Fill the cell with 1.5 mL of the prepared stock solution containing the sample. Place the cell in the holder and press "measure." The machine readout will give the optical rotation value. Remember to record the temperature as well. 4. Calculation of Specific Rotation The specific rotation of a compound is defined by the following equation: where α is the optical rotation value given by the polarimeter, l is the cell pathlength in dm, and c is the concentration of the solution in g/mL.