Midterm 2 W10

Midterm 2 W10 - Chem 6AL Russak 22 February 2010 ...

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Unformatted text preview: Chem 6AL Russak 22 February 2010 Midterm 2 The following questions are all multiple choice. Please fill out the score sheet with your name. You must put your perm number on the score sheet and fill in the bubbles associated with it to receive credit for the exam. There are equations/spectral keys on the back sheet that you may need to calculate/solve your answers. You may use a calculator. There is only 1 correct choice for each question, filling in multiple answers will result in no credit given. Please keep this question sheet as a record of your exam and turn in the scantron only. There are 40 questions. Thin Layer Chromatography 1. In Thin Layer Chromatography, which technique of visualization is destructive to the compound? a. Visible detection b. Iodine stain c. UV detection d. KMNO4 stain e. None of the above are destructive 2. Determine the plausible reason all spots should be forced to travel at least partially up the TLC plate during development. a. There is no reason why all spots have to travel, just as long as they separate b. To decrease the resolution c. To prove that there aren’t any other spots underneath d. To allow time for the solvent to reach the top of the plate e. None of the above 3. Which of the following is not an adsorbent used in TLC a. Alumina b. Sodium Sulfate c. Silica Gel d. Cellulose e. B and D 4. Regarding the TLC in the next question, let’s say that a mixture of 2:1 hexanes:ethyl acetate was used to develop the plate. What would happen to the spots if a 3:1 mixture of hexanes:ethyl acetate was used? a. The solvent mixture is less polar so all spots would travel more b. The solvent mixture is more polar so all spots will travel more c. Compound A will travel further while compound B will be retained d. Compound B will travel further while compound A will be retained e. All spots will travel less 5. Consider the following TLC below: The TLC of reaction A B tells you that: a. Starting material is not currently present in the reaction b. The reaction is incomplete c. The spot in lane C is less polar that lane A d. The spot in lane A is more polar than lane C e. None of the above Infrared Spectroscopy 6. When performing an IR, a salt plate is used to put the sample on. What must be a characteristic of this plate? a. It transmits in the infrared spectrum b. It interacts with the sample to induce infrared absorptions c. It is a purely covalent material d. All types of light can pass through it without refraction e. None of the above 7. Which compound would have the highest C=O wavenumber? a. Cyclobutanone b. Cyclopentanone c. Cyclohexanone d. Cycloheptanone e. None of the above 8. Look at the structure of the following molecule and choose the answer that shows the stretches that would be present O NH2 a. b. c. d. e. 3100, 2900, 1715 3400, 3100, 1715 3400, 2900, 1690 3100, 2900, 1750 None of the above Match the following compounds to their Infrared Spectra: O OH O O A B C D E 9. 10. 11. 12. 13. Experiment 5 14. In the photoisomerization experiment, what is the driving force of the reaction? a. The light shining in on the compound that causes isomerization b. The crystallization of the cis isomer c. The crystallization of the trans isomer d. The solvent used to dissolve the starting material e. None of the above Experiment 6 15. In experiment 6, which compound is more polar? a. 4 ­tert ­butylcyclohexanone b. trans ­4 ­tert ­butylcyclohexanol c. cis ­4 ­tert ­butylcyclohexanol d. dichloromethane e. None of the above 16. When a reaction proceeds as in experiment 6 with respect to stereochemistry, it is said to be a. Racemic b. Stereogenic c. Stereospecific d. Stereoselective e. None of the above Experiment 7 17. Even though potassium carbonate does not seem to be strong enough pKa ­wise to affect the equilibrium in the product direction, what allows the reaction to proceed? a. The subsequent loss of carbon dioxide b. The subsequent loss of iodine c. The phenol is able to substitute iodine without deprotonation d. The donating nature of the amide functional group assists in the nucleophilicity of the phenol e. None of the above 18. After the MEK was removed, an extraction using NaOH as the aqueous phase was performed. Why? a. To remove any excess MEK from the product b. To partition the product into the aqueous layer c. To partition any remaining starting material in the aqueous layer d. To generate the suitable phenoxide needed for ether formation e. None of the above 1H NMR Spectroscopy 19. What is the internal standard used in 1H NMR spectroscopy? a. D2O b. Si(CH3)4 c. C(SiH3)4 d. CCl4 e. None of the above 20. What would be within the typical concentration range for an NMR sample? a. 10 mg in 5 mL of CHCl3 b. 10 mg in 0.5 mL of CHCl3 c. 20 mg in 0.5 mL of CDCl3 d. B and C e. None of the above 21. What ensures that an NMR sample is homogenous when acquiring a spectra? a. Spinning the sample b. Shaking to mix the sample c. Ensuring that the sample is not completely dissolved d. Shimming the NMR magnet e. None of the above 22. What does the “FT” in FT NMR stand for? a. Free Transform b. Fourier Transform c. Free Transduction d. Freezing Temperature e. None of the above 23. An aldehyde hydrogen is said to be ________ compared to an aromatic hydrogen a. Upfield b. Downfield c. Shielded d. Electron Rich e. None of the above Determine the number of non ­equivalent hydrogen nuclei in the following structures: 24. H2N a. b. c. d. e. 2 3 4 5 None of the above O 25. a. b. c. d. e. O 3 4 5 6 None of the above 26. a. b. c. d. e. 1 2 3 4 None of the above Match the following structures to their 1H NMR Spectra: s=singlet, d=doublet, t=triplet, q=quartet, qt= quintet, sx=sextet, st=septet, ot=octet, m=multiplet (multiplet signals are overlapped and difficult to determine splitting). The integrations are given in parentheses next to the splitting pattern. Match the following structures to their 1H NMR spectra: O OH O O A B C D E 27. q(2H), t(3H) 28. t(2H),s(1H),m(4H),t(3H) 29. t(2H),s(3H),sx(2H),t(3H) 30. t(2H), qt(2H) m(5H), s(1H) C13 NMR Spectroscopy Determine the number of non ­equivalent carbon nuclei in the following structure: 31. 32. a. b. c. d. e. 2 3 4 5 None of the above 33. a. 2 b. 3 c. 4 d. 5 e. None of the above 34. An alkane carbon is said to be ________compared to an alpha carbon of a carbonyl. a. Upfield b. Downfield c. Shielded d. A and C e. None of the above 35. Carbon nuclei, compared to hydrogen nuclei that are directly attached, are usually observed at ____ times the hydrogen nuclei signal in ppm. a. 5 b. 10 c. 20 d. 100 e. None of the above Match the following structures to their 13C NMR spectra: H OH O O A B C D E 36. 3 signals 37. 4 signals 38. 5 signals 39. 5 signals 40. 5 signals ...
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This note was uploaded on 04/09/2010 for the course CHEM 6a taught by Professor Pettus during the Winter '07 term at UCSB.

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