Experiment F - Lab Worksheet 2023

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Dec 6, 2023

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Lab Worksheet for Experiment F – Nucleophilic Substitution Lab 12 A, 2023 Name: ____________________________________ Section Number: _________ Part I – Prelab: (1) Predict the product in the reactions below. Draw a balanced reaction equation with a chemical structure or write NR. Next to each structure, mark S N 1 or S N 2 and fast, medium or slow to predict the dominant mechanism and kinetics. Alkyl Halide Reaction with NaI in Acetone Reaction with AgNO 3 in Ethanol 1-bromopentane 1-chloropentane 2-bromopentane 3-bromopentane 1-bromo-2-methylpropane 2-chloro-2-methylpropane 1-bromo-2,2-dimethylpropane bromocyclopentane bromocyclohexane 1-bromoadamantane 1-chloroadamantane

(2) Label H a and H b in each of the following structures as diastereotopic, enantiotopic, or equivalent. This is discussed in Section 16.4 of Karty. (3) Consider the molecule below: a. What is the relationship between H c and H d and H e ? b. What is the relationship between CH 3 (H c , H d , H e ) and CH 3 (H f , H g , H h )? c. How many chemically distinct hydrogens are there? d. What splitting pattern would you expect for each unique set of hydrogens?

(4) Data Processing Tutorial – Annotation of the 1 H NMR spectrum of 1-bromopentane. 1. Open the 1-bromopentane example NMR file according to the guidelines titled “ How to Open NMR Files in MNOVA ” under the -NMR Resources- Module on bCourses. 2. Practice zooming in and out on the spectrum using your mouse and the tools described below. a. Scrolling up and down with the mouse will change the peak heights b. There is a row of icons across the top of the screen to help with zooming. Click on them to toggle turning t hem on/off. These commands can also be found in the lower half of the “View” menu. c. Try using each of these tools. For example, if the icon is active , dragging your mouse (left click- drag-release) across a region of the spectrum will zoom in on that section of the spectrum. d. Zoom back out to the full spectrum by clicking . 3. Zoom in on the peak near 0 ppm. This peak is TMS (tetramethylsilane), which is present in the sample as an internal standard . Click on “ Analysis > Reference > Reference ” from the menus at the top of the screen. A red crosshair should appear (see screenshot below). Hover over the peak then click to select it. A menu box should pop up. Type “0 ppm” in the “new shift” field , then click OK. This resets the x-axis so that the TMS peak is exactly at 0 ppm. 4. Click on “ Edit>Annotate > Text ” and use this tool to place a textbox label above the peak labeled “ TMS ” . Exit the textbox by clicking elsewhere on the spectrum. If necessary, you can adjust the position of the textbox by selecting it (green squares will indicate that it is selected) and then dragging it to a new position. The center of each textbox will stay anchored to its position on the spectrum as you zoom in and out. 5. Zoom back out to the full spectrum by clicking 6. Zoom in on the peak near 7.26 ppm. This peak is the residual solvent peak (CHCl 3 ) that is present because the solvent used to dissolve this sample (CDCl 3 ) is not 100% deuterated. You can read about this on page 167 of the Pedersen lab manual. Annotate this peak with a textbox labeled “ CHCl 3 ” 7. Zoom in on the region of the spectrum containing the resonances of interest (4 ppm to 0 ppm) and adjust the height of the peaks so that the tallest one reaches almost to the top of the screen. 8. Click on “ Analysis > Integration > Manual ” from the menu. This turns on the integration tool. Click -drag across each peak. The program will calculate the relative area under each peak and display an integral label underneath the peak.

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9. Hover over the horizontal green bar portion of the integral label (created in step 8) for the peak at 3.4 ppm. The line should light up if your mouse is in the right place. Right click, then select “ Edit integral ” from the menu that pops up. This should bring up the “Integral Manager” box. 10. By default, the first region of the spectrum that you integrated is assigned a relative value of 1. However, this resonance might correspond to a different number of 1 H nuclei than the default value. The resonance at 3.4 ppm corresponds to two hydrogen atoms which are equivalent to each other. Type “2” in the “Normalized” field, and then close the integral manager window. All the other integral fields will automatically update relative to the new value that you set. 11. Use the textbox tool to add letter labels (A-E) just above each resonance on the spectrum, corresponding to the labels in the picture below. (Note that two of the resonances which are not identical to each other are similar enough that they overlap, so place both corresponding letters over that region of the spectrum. 12. Click on “Analysis > Peak Picking > Peak by Peak”. Hover over the center of each multiplet, one at a time, and click to label the peak. These labels (chemical shift in ppm) will appear across the top of the page. 13. Zoom back out, and then select a reasonable spectrum width and height to display which includes all your annotations (including the CHCl 3 and TMS labels). 14. Add a textbox underneath the title of the spectrum. Type your name, lab section number, an d GSI’s name . 15. Print out the spectrum and bring it to your lab section as part of this prelab. You will receive a grade on this annotated spectrum.

(5) Use MNova to print out spectra of: 1. Your crop A. 2. Your crop B. 3. Standard Salicylic acid 4. Standard Adipic Acid. Follow a similar procedure as you used in the Data Processing Tutorial from the Prelab of Lab E Asymmetric Transfer Hydrogenation. Make sure to include in each spectrum: 1. Integration 2. Peak pick 3. Print out of enlarged regions so that you can see all peaks and all coupling. Print out all four spectra and attach them to this worksheet. You will receive points for the spectra.

Part II – During and after Lab: (5) Fill out the following table with your observations of the reactions and draw the structures of the starting materials. If there was a precipitate, write all the products in the box and note the time and temperature at which the precipitate appeared. Next to your data, note whether a partner group observed the same outcome (columns labeled “Comparison”) , and mark any differences. Write the names of the people in the group you compared data with here: __________________________ Alkyl Halide Reaction with NaI in Acetone Comparison NaI Reaction Reaction with AgNO 3 in EtOH Comparison AgNO 3 Reaction 1: 1-bromopentane 2: 1-chloropentane 3: 2-bromopentane 4: 3-bromopentane 5: 1-bromo-2-methylpropane 6: 2-chloro-2-methylpropane 7: 1-bromo-2,2- dimethylpropane 8: bromocyclopentane 9: bromocyclohexane 10: 1-bromoadamantane 11: 1-chloroadamantane

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(6) Use the data from the previous table to place data points in the following two graphs. Use the row number from the previous table as the compound number, and mark similarities and differences between compounds underneath the graph (i.e. 1°, 2°, 3° carbon, rings, adamantly, neopentyl, Br/Cl). Compare your results to the class results and mark any significant differences in the graph.

(7) Compare your results to those of the class and list any possible explanations for the differences: (8) Based on the occurrence and kinetics of the reactions, compare the reactivities of various substrates for both S N 1 and S N 2 reactions. For example, consider issues such as the nature of the halide leaving group (chloride versus bromide) and the structures of the alkyl groups. Include a discussion of the effect of the temperature on the reactions observed. (9) If the reactivity differs from what you predicted, explain how the results helped you rethink your predictions. (10) To aid in the analysis of your results, draw models of the intermediate you could expect to generate in the S N 1 reaction of 1-bromoadamantane. Explain why the results from the adamantane derivatives are surprising.

(11) The reaction of alkyl bromides with sodium iodide to give alkyl iodides is typically endothermic. Explain why you observed products from these reactions despite the reactions being endothermic. (12) Summarize, in one sentence, the experimental and analytical work that you did today; and in another sentence, summarize what you have learned.

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