Midterm_2_F09_Key - Chem 6AL Russak 16 November 2009...

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Unformatted text preview: Chem 6AL Russak 16 November 2009 Midterm 2 Key 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. 1. In Gas Chromatography, compounds generally separate based on: a. Affinity for stationary phase b. Temperature of sample c. Flow rate of the carrier gas d. Boiling point e. All of the above 2. In order to separate a mixture of polar compounds by gas chromatography, what liquid column coating would you choose? a. Polysiloxanes with hydrocarbon side chains b. Diatomaceous earth with a very small particle size c. Polyethylene glycol d. Silica gel e. None of the above 3. 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 4. What is not a type of stationary phase a. Silica Gel b. Magnesium Oxide c. Cellulose d. C ­18 modified silica gel e. None of the above 5. Place the following solvents in order of lowest to highest polarity a. Ethyl acetate, hexanes, acetone, water b. Water, ethyl acetate, acetone, hexanes c. Hexanes, ethyl acetate, water, acetone d. Hexanes, ethyl acetate, acetone, water e. None of the above 6. Consider the following TLC below: Lane A is the starting material for a reaction. Lane B is the co ­spot of A and C. Lane C is the crude product obtained at the end of the reaction. According to the TLC: a. The product is less polar than the starting material b. The co ­spot claims the reaction is 50% complete c. The reaction is complete d. The reaction is incomplete and needs more time e. None of the above 7. Regarding the TLC from above, let’s say that a mixture of 5:1 hexanes:ethyl acetate was used to develop the plate. What would happen to the spots if a 4:1 mixture of hexanes:ethyl acetate was used? a. The solvent mixture is more polar so all spots would travel further b. The solvent mixture is less 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 8. 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 9. In the electromagnetic spectrum, __________ frequencies, __________ wavenumbers, and __________ wavelengths are associated with high energy. a. high, small, long b. low, large, short c. low, small, short d. high, large, short e. high, small, short 10. What functionality has the highest C=O wavelength? a. Ester b. Amide c. Aldehyde d. Ketone e. None of the above 11. You have two aromatic compounds with substituents of the same functional group, but they differ in their position on the ring. What would be the best method of characterization? a. Melting Point b. Infrared Spectroscopy c. Nuclear Magnetic Resonance d. Refractive Index e. None of the above 12. You have two constitutional isomers that contain the same functional groups. What is the best way to determine which structure is which? a. Gas Chromatography b. Infrared Spectroscopy c. Melting point d. Mass Spectrometry e. None of the above Experiment 5 13. 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 14. In experiment 6, which compound is more polar? a. 4 ­tert ­butylcyclohexanone b. trans ­4 ­tert ­butylcyclohexanol c. cis ­4 ­tert ­butylcyclohexanol d. Methanol e. None of the above 15. When a reaction proceeds with only 1 isomer as its results, the reaction is said to be a. Stereoelectronic b. Stereogenic c. Stereospecific d. Stereoselective e. None of the above Experiment 7 16. Which compound is known as Tylenol? a. The intermediate formed in the reaction b. The starting material c. The product d. Phenacetin e. None of the above 17. 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 dissolve the product into the aqueous layer c. To dissolve 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 18. What is the internal standard used in 1H NMR spectroscopy? a. D2O b. Trichloromethylsilane c. Tetramethylsilane d. CCl4 e. None of the above Determine the number of non ­equivalent hydrogen nuclei in the following structure: O 19. a. b. c. d. e. 3 4 5 6 None of the above NH2 20. a. b. c. d. e. 4 5 6 7 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 givin in parentheses next to the splitting pattern. Match the following structures to their 1H NMR spectra: 21. q(1H), s(6H), d(3H) D 22. singlet. No integration because there is only 1 peak. Integration only compares peaks to each other. C 23. st(1H),s(3H),d(6H) A 24. 2H),t(3H) E d(2H),s(1H),s(1H),qt(1H),qt( C13 NMR Spectroscopy Determine the number of non ­equivalent carbon nuclei in the following structure: 25. t(2H),s(3H),t(2H),qt(2H),s(2H) B 26. a. b. c. d. e. 4 5 7 8 None of the above O O O 27. a. 2 b. 3 c. 4 d. 5 e. None of the above Match the following structures to their 13C NMR spectra: 28. 4 signals E 29. 4 signals B 30. 3 signals C 31. 4 signals A 32. 3 signals D Mass Spectrometry 33. A compound is injected into the mass spec to give a molecular ion peak at 150. If the compound has 2 oxygen atoms, use the rule of 13 to determine the molecular formula? a. C11H18O2 b. C10H16O2 c. C10H14O2 d. C9H10O2 e. None of the above 34. How many degrees of unsaturation are present in the above compound? a. 2 b. 3 c. 4 d. 5 e. 6 35. What is a characteristic peak of mono alkyl ­substituted benzene rings? a. Acylium ion at 91 b. Acylium ion at 43 c. Tropylium ion at 91 d. Tropylium ion at 43 e. None of the above 36. What is the preferred fragmentation of the following molecule given the mass spectra? HO a. HO CH3 HO b. H O c. H O CH3 d. CH2CH3 e. None of the above The fragment is not a cation radical, so d would be right if it had 1 more electron. ...
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