Lab 6 Orgo / Experiment 7: Polarimetric Analysis Of Organic Compounds PDF

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Experiment 7: Polarimetric Analysis of Organic Compounds Dzeneta Pajazetovic TA: Nan November 8, 2017

Introduction: The purpose of this experiment is to become familiar with using a polarimeter and to use optical rotation as a method of determining the identity of unknown sugars. Polarimetry is used in many ways like dealing with process control in the pharmaceutical industry, flavor, fragrance and essential oil industry, food industry, or chemical industry. To find the optical purity of the product, it can be determined by measuring the specific rotation of compounds like amino acids, antibiotics, or steroids and comparing them to with reference values. For this lab polarimetry is used to determine the specific rotation of a sample containing limonene and then using that data to determine its optical purity. When regular light passes through a polarizer, only the light-wave components that are parallel to the plane of the polarizer can pass through. The beam that results from this passing has light waves whose vibrations are restricted to a single plane. When the beam passes through an optically active substance, molecules of the substance interact with the light so it will rotate its plane of polarization. The angle that the sample of an optically active substance rotates the plane of that beam is called the observed rotation. Also the measurement of those angles of rotations is polarimetry and the instrument that measures them is a polarimeter. The observed rotation depends on the length of light path through the sample and the concentration of the sample along with its identity. To determine the specific rotation of an optically active sample, a polarimeter is used and the optical rotation of a substance is usually measured in solution.

Procedure and Observations: In this experiment, it was shown how to become familiar with using a polarimeter and how to use optical rotation as a method of determining the identity of unknown sugars. The ability to rotate light is optical activity. The degree that a substance rotates light can be used to determine the identity of the substance, the enantiomeric purity of the substance, and the concentration of a known substance in a solution. Polarimetry was used to determine specific rotation of a sample containing limonene. The assigned unknown was determined to be D-Fructose with a specific rotation of -92. Personal Protective Equipment was to be worn at all times. This includes gloves, apron, safety goggles, and appropriate clothing and

shoes. All the chemicals are potentially toxic upon ingestion so avoid contact of the chemicals with skin and eyes. Use extreme caution and work in the fume hood. Always review SDS sheet for all the chemicals being used in each experiment. Though aqueous sugar solutions are nontoxic and polarimeter have no special hazards, still try to use caution when around them. In case of skin contact, flush area with cold tap water for 15 minutes and warn TA for further actions. Data and Calculations: Identification Letter for Unknown Sugar Compound Concentration Cell length (l) in dm (c)g/ml 5% unknown A 5%=0.05g/mL 1dm 10%= .1g/mL 1dm 10% known D fructose

Observed rotation (a) 4.67 9.2

Direction of rotation (+/-) -

Results: In this experiment, the specific rotation of a sugar solution was calculated and the identity of the sugar was determined. The degrees and direction of optical rotation of the unknown assigned was -4.67. Then the concentration (g/mL) of the sample was calculated which ended up being .05g/mL. The specific rotation was determined to be -92 of the unknown which lead to the conclusion that the unknown was D-fructose by comparison of literature values. Then 10mL of the known solution that was determined was obtained and the optical rotation was found. The optical rotation is -9.2 and with that the specific rotation of the solution was determined to be -92. Discussion: All the objectives in this experiment were met. Using techniques from a polarimeter and optical rotation, the specific rotation and identity of an unknown sugar was found. The given unknown solution had an observed rotation value of -4.67 and a path length of 1dm and concentration of .05g/mL. When the specific rotation was calculated, it matched the literature value of D-Fructose which was -92 and this is how the sugar was identified. Once it was identified, then the optical rotation was found to be -9.2. By having the optical rotation value, the specific rotation could be determined and the optical purity as well. The specific rotation of a compound is a fixed physical property of that compound. The observed rotation depends on the concentration of the sample in solution and the length of the cell as well as the specific optical rotation of the compound. Also if you were to double the concentration of a material in a solution, it will double the observed rotation. Cutting the cell length in half will half the observed rotation. The specific rotation remains the same regardless of the concentration or cell length. From the experiment, it was shown that experimenters had learned how to successfully use a polarimeter and optical rotation as a method of determining the identity of unknown sugars. These techniques made it possible to identify the substance, the enantiomeric purity of the substance and the concentration of a known substance in solution. In this experiment the techniques also made it possible to obtain the observed rotation and to use these calculated values to determine the specific rotation and identity. A change that could be made for more accurate experiments would be to provide a more accurate way of reading the measurements....