TLC, IR, MP TEMPLATE

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Feb 20, 2024

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NEW TEMPLATE: TLC, FTIR, AND MELTING POINT Pre-lab Questions Procedure and Safety 1. (10 pts) Write a VERY brief bullet point list summary of the procedure. The point of this is to make sure you read and understand the procedure. You do not need to include every detail. TLC= use 3 jars (100 hexanes, 85% hexanes/15%ethyl acetate 10%ethyl acetate) Prepare and spot the plate, add to jar, wait, visualize using UV light. Do same with our compounds but with the 85%/15% mix. FTIR=Run computer program MELTING POINTS= Find melting point, use the machine like in intro lab 2. (4 pts) To prepare 10 mL of a 80% hexanes/20 % ethyl acetate developing solvent, 8 mL of hexanes is measured in a 10 mL graduated cylinder and then 2 mL of ethyl acetate is added. Explain how to prepare 10 mL of a 85% hexanes/15% ethyl acetate developing solvent. 8.5ml of hexane and 1.5ml of ethyl acetate. 3. (4 pts) Write one sentence summarizing the safety concerns for this experiment. Everything used in this experiment is toxic or hazardous in some way. 4. (4 pts) What do you need to be careful of when picking up a TLC spotter? Where should spotters be put when you are finished? In the glass receptacle. Part 1: Choosing the best developing solvent for TLC 5. (15 pts total, 5 pts each structure, 5 pts picking most polar) Draw the bond-line structures of the two solids you separated, 9-fluorenone and benzoic acid. Which is more polar? Benzoic acid is more polar 6. (5 pts) Given that the surface of a silica coated TLC plate (the type we use) can be represented by the structure below, would 9-fluorenone or benzoic acid be more attracted to the TLC plate surface? Flourenone 7. (15 pts total, 5 pts ea structure, 5 pts correct labeling) In our Ochem labs, two solvents are often used for developing TLC plates: ethyl acetate and hexanes. Draw the bond-line structures for these two solvents. (Just draw one isomer of hexane). Which of these solvents is polar and which is nonpolar? Polar= ethyl acetate 8. (10 pts) As you learned in the tutorial video, “TLC Theory”, how fast a compound moves up a plate is determined by its solubility in the mobile phase (developing solvent) vs its attraction to the
stationary phase (silica). If a nonpolar solvent is used as developing solvent, would you predict 9- fluorenone or benzoic acid moves up the TLC faster? Why? Benzoic acid is nonpolar and more attracted to the polar TLC plate. 9. (4 pts) Consider the photo below showing TLC plates from a different experiment. Which plate shows the best separation for the four different compounds that were spotted? Part 2: Functional groups and interpreting FTIR spectra 10. (40 pts, 4 pts each name, 4 pts each peak) Fill in the following table. Compound Structure Functional Group Name Location of key IR peaks (cm -1 ) alkenes 1680-1600 Hydroxyl/alcohols 3650-3200 Carboxyl/ ketones 1780-1650 Carboxyl/ carboxylic acids 3300-2500 Benzene ring/aromatics 1600-1430 11. (8 pts) What are the functional groups in 9-fluorenone? Predict the two main peaks you will see above 1500 cm -1 in the FTIR spectrum for 9-fluorenone. Plate A Plate B Plate C
Ketone and benzine ring/aromatics 12. (12 pts) What are the functional groups in benzoic acid? Predict the three main peaks you will see above 1500 cm -1 in the FTIR spectrum for benzoic acid. Carboxylic acids, benzne ring, ketones or alkenes Data and Observations Part 1: TLC 1. (15 pts) Insert a photo of your three TLC plates used for testing developing solvents with provided solutions of benzoic acid and 9-fluorenone. The solvent front should be marked and circles drawn around any spots visualized using UV light. Plates should be clearly labeled with developing solvent used and what was spotted. Photo should include a ruler for calculating R f values. 2. (15 pts) Insert a photo of the TLC plate showing results from your separated benzoic acid. The solvent front should be marked and circles drawn around any spots visualized using UV light. Plates should be clearly labeled with developing solvent used and what was spotted. Photo should include a ruler for calculating R f values. 3. (15 pts) Insert a photo of the TLC plate showing results from your separated 9-fluorenone The solvent front should be marked and circles drawn around any spots visualized using UV light. Plates should be clearly labeled with developing solvent used and what was spotted. Photo should include a ruler for calculating R f values. Part 2: FTIR
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4. (20 pts) Insert a photo of your FTIR spectrum for your separated benzoic acid. Draw the structure of benzoic acid on or near the spectrum. Label the peaks in the spectrum which correspond to functional groups in benzoic acid. 5. (20 pts) Insert a photo of your FTIR spectrum for your separated 9-fluorenone. Draw the structure of 9-fluorenone on or near the spectrum. Label the peaks in the spectrum which correspond to functional groups in 9-fluorenone.
Part 3: Melting Points (don’t forget units) 6. (5 pts) Melting Point of your separated benzoic acid 103-109 C ___________ 7. (5 pts) Melting Point of your separated 9-fluorenone 71-78 C____________ Analysis and Application Questions Analysis 1. (8 pts, 4 pts choice, 4 pts explanation) Examine the photo that you inserted in Data and Observations question 1. Which solvent resulted in the best separation for benzoic acid and 9- fluorenone? Write one sentence to explain why. 15% ethyl 85% hexane, R f Values Review (Also explained in TLC Theory Tutorial Video) The R f value describes the distance a given compound traveled a relative to the distance the solvent traveled. Example: The sample spotted on the TLC plate below contains 3 compounds. The R f values for components A and B are calculated. R f = distance traveled by the substance distance traveled by the solvent
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2. (6 pts) Calculate the R f values for the spots on the TLC plate that showed the best separation. Show your work. .8 3. (10 pts) Calculate the R f values for the spots on the TLC plates for your separated Benzoic acid and 9-fluorenone . Show your work. B = 2.5/5.4=.46 F = 2.5/5.9=1 4. (30 pts, 5 pts for specifically explaining how each type of data supports claim for each compound) Was your separation of benzoic acid and 9-fluorenone successful? Explain. Use your TLC, FTIR, and melting point data as evidence in your explanation. The TLC shows similar results between the pure and extracted Benzoic and 9-Flourenone, as does our melting points. The Benzoic acid FTIR shows a peak around 1600 which is consistent with the aromatics and also possibly a peak around 2800 showing an alkane. The 9 fluorenone FTIR shows a clear aromatic peak at 1600 but a weak peak around 3000. Due to the FTIR’s being slightly off I would say our extraction was correct but maybe had issues that prevented them from being pure. Hint: You need to be specific when using data as evidence. For example, “My spectrum of 9 - fluorenone has a peak at 1750 cm -1 . This is the expected peak for a carbonyl group which is consistent with the carbonyl functional group of 9-fluorenone. The spectrum also has weak “teeth” 1800-2000 cm -2 which is consistent with the aromatic rings in 9- fluorenone.” Saying, “My spectrum is constistant with what is expected for 9 - fluorenone.” without any additional explanation is not a sufficient answer. If you need more guidance, ask your TA or instructor for suggestions before submitting your lab report. Application 5. (5 pts) Aldehydes, ketones, and carboxylic acids all have a strong IR peak around 1750 cm -1 . Using the structures that you drew and table of IR stretching frequencies provided in the introduction, explain why this is so. Because of the double bond. 6. (5 pts) Both carboxylic acid and alcohol functional groups have a strong broad peak around 3000 cm -1 due to -OH. Explain how to tell the difference between an alcohol and carboxylic acid FTIR spectrum. Carboxylic acids will be more broad than alcohols 0 1 2 3 4 5 6 7 9 8 10 11 solvent front Component A Component B Component C initial spot R f = distance traveled by the substance distance traveled by the solvent R f = R f = R f = R f = 6 units 8 units 4 units 8 units 0.75 0.50 A and B Answer:
7. (10 pts) TLC is used in the pharmaceutical industry to detect impurities in a synthesized drug. The following photo shows a limit test of a steroid synthesis while the synthesis is still going on. (reference: https://www.sciencedirect.com/science/article/pii/S0021967310017206?via%3Dihub ) For this synthesis, a maximum of 1 of contaminating starting material is allowed to remain when the reaction is stopped. Based on the results shown in the TLC plate above, would you stop the reaction or not? Explain your answer based on the patterns of spots shown in the reaction mixture compared to the spots showing pure starting material. (Be sure to read the caption for the photo or you will not be able to answer this question.) It looks like the mixture is the same color as the 1 of contamination, implying that the one being tested is not fit.