TLC and NMR Spring 2017 Renan Gongora TLC and NMR: Outline TLC Motivation Background Experiment NMR Motivation Background Experiment Motivation: Thin Layer
Chromatography (TLC) Track Purification Method Qualitative Product Purity Track Reaction Progress 3 TLC: Motivation To establish that two compounds are identical
To determine the number of components in a mixture To determine the appropriate solvent for a column-chromatographic separation To monitor a column-chromatographic separation To check the effectiveness of a separation achieved on a column, by crystallization or by extraction To monitor the progress of a reaction Chromatography Parameters that affect separation Adsorbate choice
Solvent polarity Chromatography: Background 6 Chromatography: Experiment A X MODIFICATION: NO fluorenol X 7 Chromatography: Experiment A
Reaction mixture: spot both fluorene and fluorenone 8 Chromatography: Experiment A Obtain four capillary tubes to spot the plate. Prepare a TLC development chamber with methylene chloride A beaker covered with aluminum foil or a wide-mouth. Be sure that the filter paper liner does not go completely around the inside of the container. Spot fluorene, fluorenone, the unknown (mixture or pure) and the standard reference mixture, which contains both compounds. For each of the four samples, use a different capillary tube to spot the sample on the plate.
Take up part of the sample in the capillary tube and apply to the dull side of the plate. The spot should be no larger than 2 mm in diameter. It will usually be sufficient to spot each sample once or twice ONLY!!. 9 Chromatography Experiment A Place the TLC plate in the development chamber, making sure that the plate does not come in contact with the filter paper liner. Remove the plate when the solvent front is 12 cm from the top of the plate. Mark the position of the solvent front. When the plate is dry, place the plate in a
jar containing a few iodine crystals and cap the jar. Remove the plate from the jar and lightly outline all the spots that became visible with the iodine treatment. 10 Chromatography Experiment A: What to Report? Measure the distance that each spot has traveled relative to the solvent front. Calculate the Rf values for each spot. Explain the relative positions of the three compounds in terms of their polarities. Identify the compound or compounds that are found in the
unknown mixture. THROWAWAY ALL TLC PLATES NONE SHOULD BE GIVEN TO THE GTA OR SUBMITTED IN THE NOTEBOOK ( 5pts for any plates put into the notebook) 11 Chromatography Experiment C O WHAT IS t for this reaction? OH NaBH 4 MeOH, t
Prepare two thin-layer plates in the same way as you did in Part A When you mark them with a pencil for spotting, make five marks 1 cm apart on the first plate and four marks on the second plate. During the reaction, you will be taking five samples from the reaction mixture at 0, 15, 30, 60, and 120 seconds. In addition, each plate should be spotted with a reference solution containing fluorenone. Indicate at the top of each plate where each sample will be spotted so that you can keep track of them. Write the number of seconds and an abbreviation for the two reference compounds. Use the same TLC development chamber with methylene chloride that you used in Part A. Prepare six capillary tubes to spot 12 the plates. ChromatographyO Experiment C OH
NaBH 4 MeOH, t 25C Running the Reaction. Once sodium borohydride has been added to the reaction mixture (see next paragraph), take samples at the times just indicated. T5 T4 T3 T2 Spot each sample once, using a different pipet for each sample.
T1 Fluorenone Because this must be done in such a short time, you must be well prepared before starting the reaction. One person should be the timekeeper, and the other person should take the samples and spot the plates. Place a magnetic stirring bar into a 25-mL Erlenmeyer flask. Add 0.40 g of fluorenone and 8 mL of methanol to the flask. Place the flask on a magnetic stirrer. Stir the mixture until all the solid has dissolved. Now take the first sample (the 0 second sample) and spot the plate. 13 ChromatographyO Experiment C
OH NaBH 4 MeOH, t Weigh 0.040 g of sodium borohydride and immediately add it to the reaction mixture. If you wait too long to add it, the sodium borohydride will become sticky, as it absorbs moisture from the air. T5 T4 T3 T2
T1 Fluorenone Begin timing the reaction as soon as the sodium borohydride is added. Use the capillary tubes to remove samples of the reaction mixture at the following times: 15, 30, 60, and 150 seconds. Use a different capillary tube each time and spot a TLC plate with each sample. After developing the plates and allowing them to dry, visualize the spots with iodine, as described in Part A. Make a sketch of your plates and record the results in your notebook. Do these results indicate that the reaction went to completion? In addition to the TLC results, what other 14 visible evidence indicated that the reaction went to completion? Explain.
Chromatography Experiment C: (what to report?) O OH NaBH 4 MeOH, t Weigh 0.040 g of sodium borohydride and immediately add it to the reaction mixture. If you wait too long to add it, the sodium borohydride will become sticky, as it absorbs moisture from the air. T5 T4
T3 T2 T1 Fluorenone Begin timing the reaction as soon as the sodium borohydride is added. Use the capillary tubes to remove samples of the reaction mixture at the following times: 15, 30, 60, and 150 seconds. Use a different capillary tube each time and spot a TLC plate with each sample. After developing the plates and allowing them to dry, visualize the spots with iodine, as described in Part A. Make a sketch of your plates and record the results in your notebook. Do these results
indicate that the reaction went to completion? In addition to the TLC results, what other 15 visible evidence indicated that the reaction went to completion? Explain. TLC and NMR: Outline TLC Motivation Background Experiment NMR Motivation Background Experiment NMR Spectroscopy: Motivation
Determines the carbon hydrogen framework in addition to determining most functional groups Spectroscopy: Flow Chart Spectra DETECTION MOLECULAR RESPONSE EXCITATION E=hv Unknown or known sample 18
Excitation Strength of the magnet determines the range and provides separation Molecule to absorb pulses of radiation in FT-NMR 19 Molecular Response Dont memorize equations (you wont be quizzed on
this) 20 Terminology Nucleus Deshielded Environment Shielded d- RO Spectra obtained from the spectral organic d+
C H 21 Terminology d- Spectra Downfield Upfield
RO Spectra obtained from the spectral organic d+ C H 22 NMR Spectroscopy: Experiment Add 30 mg of your unknown sample to a 25 mL flask. Use a Pasteur pipet to transfer about 0.5 mL of the deuterated chloroform to your
sample. Swirl the test tube or conical vial to help dissolve the sample. At this point, the sample should have completely dissolved and transfer this solution to the NMR tube. The height of the solution in the NMR tube should be approximately three fingers width. Cap the NMR tube. Do this firmly but not too tightly. If you jam the cap on, you may have trouble removing it later without breaking the end off of the very thin glass tube. Make sure that the cap is on straight. DO NOT INVERT NMR TUBE NMR Spectroscopy: Experiment You will label your NMR tube and the GTA will run and process the NMR for you. This is important so that you receive you NMR spectra for your sample (via email [write that down too]). You will be cleaning this NMR tube next week and
then preparing your sample (benzoin) for NMR. NMR Spectroscopy: Experiment (what to report)? Unknown All Important NMR peaks (experimental) This includes: Chemical shift/ ppm All SDBS peaks (fluorene) Integration Values Assignments All SDBS peaks (fluorenone) Multiplicities
Still confused???? See the Klein Text, the NMR reference section in the lab manual or the video on the website and the example In the results section of the syllabus This will help you report the unknown ratio (if there is a mixture of compounds) of fluorene to fluorenone. This will also be in agreement with your TLC plate.
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