Final W10 Key

Final W10 Key - Chem 6AL Russak 17 March 2010 7:30...

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Unformatted text preview: Chem 6AL Russak 17 March 2010 7:30 ­10:30 pm Final Exam KEY The following questions are all multiple choice. Please fill out the score sheet with your name and perm number. Your perm number MUST be both written and the bubbles filled. There are equations and spectral charts on the back sheets that you may need to calculate or solve your answers. You may use a simple scientific calculator, ruler, and pencil or pen. Experiment 1: Density, melting point, refractive index 1. The refractive index of diamond is 2.4. What is the speed of light through diamond? a. 1.25 m/s b. 8 E ­9 m/s c. 8 m/s d. 1.25 E8 m/s e. None of the above 2. Refractive index is reported as nD20= value. What does the D stand for? a. The D ­line of sodium b. The angle of incidence c. The angle of refraction d. The temperature that the sample was conducted e. None of the above 3. A melting point was taken of a 20 mol % sample of cinnamic acid (148.16 g/mol) in urea (60.06 g/mol). What is this mixture in wt %? a. 9.2 wt % b. 12.0 wt % c. 25.1 wt % d. 38.1 wt % e. None of the above 4. The melting point of a compound is reported as a range. The range is representative of: a. The temperature when solid and the temperature when liquid b. The temperature of evidence of 1st drop and the temperature when liquid c. The temperature of evidence of shriveling and the temperature when liquid d. The temperature of evidence of meniscus and the temperature when liquid e. All of the above 5. In general, how do impurities affect the melting point and range? a. They increase both b. They decrease both c. Melting point increases but the range decreases d. Melting point decreases but the range increases e. None of the above 6. A student weighed a syringe with 2.3 mL of toluene inside and found it to be 5.2 grams. Considering the density of toluene is 0.87 g/mL, what was the mass of the empty syringe? a. 2.0 g b. 2.26 g c. 3.2 g d. 5.98 g e. None of the above 7. Two compounds with the same literature melting point are mixed in equal amounts. What will be the most likely outcome? a. The melting point will be the same, but the range will be broader b. The melting point will be lower and broader c. The melting point will be the same and the range will be the same d. The melting point will be lower, but the range will be sharper e. None of the above Experiment 2: Distillation, Boiling points, Rault’s law 8. What is “bumping”? a. An explosive boiling of a liquid b. When a glass joint between two pieces of glassware becomes stuck and unable to be taken apart c. When molecules collide in gas phase in the mass spec to produce a radical cation d. The point at which Rault’s law for each liquid in a mixture intersect e. None of the above 9. What is the partial pressure of a 50 mol % solution of methanol (P°=81 kPa) a. 1.62 kPa b. 20.25 kPa c. 40.5 kPa d. 61 kPa e. None of the above 10. Consider a 20 mol % mixture of hexane (P°=72 kPa) in toluene (P°=35 kPa). What is the combined vapor pressure? a. 7 kPa b. 14.4 kPa c. 28 kPa d. 42.4 kPa e. None of the above 11. From the question above, calculate the fraction of hexane molecules that reside in the vapor above the solution? a. 20 % b. 25% c. 34% d. 66 % e. None of the above 12. What is usually added to solution before beginning a distillation? a. Boiling stone b. Drying salts c. Thermometer d. Internal Standard e. None of the above 13. A fractional distillation, when compared to a simple distillation, will usually give: a. more volume of a more pure substance b. less volume of a more pure substance c. more volume of a less pure substance d. less volume of a less pure substance e. None of the above 14. Use the graph below to answer the question. How many distillations would it take for a 80/20 mixture of hexane/pentane to be greater than 98% pure in pentane? a. b. c. d. e. 1 2 3 4 Greater than 4 15. When an azeotrope occurs in a solution of liquids a. It is easy to distill the mixture to purity b. Many times column hold ­up is the cause for such an effect c. The forces of boiling the impure substance out are greater than the boiling point of the solution d. The forces of boiling the impure substance out are far less than the boiling point of the solutions e. None of the above Experiment 3: Acid/Base chemistry, Extraction, Recrystallization 16. Ethanol/water cannot be used as a pair of liquid ­liquid extraction solvents because: a. they have different boiling points b. ethanol is more polar than water c. they are immiscible d. they are miscible e. None of the above 17. Consider the following equilibrium Given that the pKa for benzoic acid is around 4 and the pKa for protonated aniline is 7, how many molecules of benzoate are there for every molecule of benzoic acid? a. 0.1 b. 10 c. 1.0 E3 d. 1.0 E4 e. None of the above 18. Which organic solvent would constitute the bottom layer when performing an extraction with water? a. Ethyl Acetate b. Hexanes c. Diethyl ether d. Toluene e. None of the above 19. The reason recrystallization works to purify a compound is because a. Impurities are highly concentrated in the solvent b. The solute is lowly concentrated in the solvent c. Impurities are lowly concentrated in the solvent d. The concentration has no effect on the ability to crystallize the compound e. None of the above Experiment 4: Extraction and coefficients 20. If dichloromethane and water are the extraction solvents, vigorous shaking can lead to: a. Evaporation b. Separation c. Byproducts d. Emulsion e. None of the above 21. What is the total % recovered after performing an extraction 2 times with equal volumes of each phase. The partition coefficient of the compound is 3. a. 3.13% b. 6.25% c. 25.0 % d. 93.8 % e. None of the above 22. How many extractions will it take to recover greater than 98% of a compound with partition coefficient of 4. You are extracting with 3 mL of ethyl acetate each time from a 5 mL volume of water. a. 1 b. 2 c. 3 d. 4 e. More than 4 Experiment 5: Photoisomerization, Thin Layer Chromatography 23. Why is the above reaction carried out with light and not heat? a. The heat required would probably decompose the compound before isomerization b. Heat would give the thermodynamically more stable product..which is trans c. Heat is unable to polarize electrons d. Heat would cause dimerization e. None of the above 24. The reaction in experiment 5 was done in homogeneous solution to start with. Why? a. Molecules in solution allow space between themselves so reactions can take place b. In a solid form, most of the trans is protected from light by the crystal lattice c. The solution provided a medium that was soluble for the starting material and insoluble for the product d. A and B e. A, B, and C 25. With respect to TLC, compounds that are non ­polar a. Travel less than polar compounds b. Travel further than polar compounds c. Are never visible under UV light d. B and C e. None of the above 26. Consider the TLC below. Lane 1 is starting material, lane 2 is a co ­spot containing both the starting material and the crude product, and lane 3 is the crude product. What can be interpreted from it? The crude product is less polar than the starting material The reaction is approximately 50% complete The separation of the compounds is not ideal The starting material is more non ­polar than the crude product None of the above 27. Consider the following TLC. The mobile phase used was 4:1 hexanes:ethyl acetate. Suggest a solvent system that would increase the separation of the spots. Assume the same about the nature of each lane as in the previous question. a. b. c. d. e. a. b. c. d. e. 100 % hexanes 2:1 hexanes: ethyl acetate 6:1 hexanes: ethyl acetate 10:1 hexanes: ethyl acetate No matter how you change the solvent, the resolution will remain the same Gas Chromatography 28. 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 29. Gas Chromatography uses a carrier gas to transport the sample through. Which is a typical carrier gas used? a. Helium b. Oxygen c. Hydrogen d. Butene e. None of the above 30. A compound elutes on the GC at 250 mm from the starting point. What is the retention time if the paper is moving 2 cm/min? a. .125 min b. 1.25 min c. 12.5 min d. 125 min e. None of the avove 31. What best describes how gas chromatography works: a. A mixture of solids are passed through a tube filled with silica gel and carried through with a liquid mobile phase b. A mixture of liquids are passed through a tube coated with polysiloxanes and carried through with a liquid mobile phase c. A mixture of solids are passed through a tube filled with silica gel and carried through with a gaseous mobile phase d. A mixture of liquids or gasses are passed through a tube coated with polysiloxanes and carried through with a gaseous mobile phase e. None of the above 32. Which of the following compounds would elute last from the GC? a. Pentane b. Propane c. Butane d. Octane e. Hexane Experiment 6 33. The starting material for experiment 6 is uniquely absent of indicated chirality. This is because a. The t ­butyl locks the ring in one conformer b. The starting material is racemic c. The structure is symmetrical and therefore does not have chirality d. All of the above e. None of the above 34. For Experiment 6, the cis Rf will be ________ as compared to trans Rf in TLC analysis. a. Larger b. Smaller c. The same d. non ­existent e. None of the above 35. The reaction in experiment 6 above is said to be a. Stereoelectronic b. Stereogenic c. Stereospecific d. Stereoselective e. None of the above Experiment 7 36. After the MEK was removed, an extraction using NaOH as the aqueous phase was used. 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 37. Assuming the pKa of the phenol in the starting material is 9 and NaOH was added to generate the conjugate base. Assuming the pKa of water is 15, the equilibrium constant should be a. 106 in favor of the phenoxide b. 106 in favor of the phenol c. 10 ­6 in favor of the phenoxide d. The reaction is in perfect equilibrium e. None of the above Miscellaneous Spectroscopy Questions 38. Infrared Spectroscopy is useful for: a. Differentiation of molecules of same functional group b. Differentiation of molecules of differing functional groups c. Determining the yield of a product d. Determining non ­equivalent protons e. None of the above 39. What type of IR motions do not typically yield an absorption? a. Asymmetric b. Symmetric c. Bending d. Twisting e. Wagging 40. The region of an IR from 1500 cm ­1 to 400 cm ­1 is known as: a. The shortwave region b. The high energy region c. The spectral region d. The fingerprint region e. None of the above 41. An IR was taken of a compound that displayed a strong peak at 1700 cm ­1 and a small peak at 3400 cm ­1. The small peak is most likely due to a. The presence of an OH stretch from a primary alcohol b. The presence of an NH stretch from an amino group c. The presence of an overtone d. The presence of a carbonyl stretch and an sp2 hybridized C ­H stretch 42. The position of a carbonyl stretch in the IR is proportional to the a. Type of functional group b. The bond order c. The bond length d. The bond strength e. None of the above 43. When an overtone band of one functional group is near a stretch of another, which phenomenon occurs? a. Anisotropy b. Fermi Resonance c. Delocalization d. Conjugation e. None of the above 44. Pertaining to the phenomenon in the above question, which functional group is known to exhibit this? a. Carboxylic acid b. Sp C ­H stretch c. Sp3 C ­H stretch d. Aldehyde e. None of the above 45. How many signals would you expect to see in the 1H NMR spectrum of the following compound? a. 1 b. 2 c. 3 d. 4 e. 5 46. How many signals would you expect to see in the 1H NMR spectrum of the following compound? a. 3 OH b. 4 c. 5 d. 6 e. 7 47. How many signals would you expect to see in the 13C NMR spectrum of the following compound? Br a. b. c. d. e. 2 3 4 5 6 O Br O 48. What splitting pattern is observed in the proton NMR spectrum for the indicated hydrogens? a. b. c. d. e. singlet doublet triplet quartet multiplet H H N O 49. There are no splitting patterns in 13C NMR spectroscopy. The reason is because: a. Carbon nuclei are not interfered with by neighboring carbon nuclei like in H NMR b. Carbon NMR obeys the N=0 rule c. The abundance of 13C is too high for splitting to be accurate d. The abundance of 13C is too low for splitting to be accurate e. None of the above 50. What is responsible for an alkene proton appearing so far downfield at 5 ­7 ppm? a. Hydrogen and carbon are electron withdrawing b. Anisotropy c. Magnetic field d. Fermi Resonance e. None of the above Infrared Spectroscopy Match the following structures to their Infrared Spectra: H NH2 N O OH O O O A B C D E 51. C 52. A 53. E 54. D 55. B 1H NMR Spectroscopy Match the following structures to their 1H NMR spectra. No integration is needed for you to solve these. O H O H O OH OH A B C D E 56. A 57. E 58. B 59. D 60. C C13 NMR Spectroscopy Match the following structures to their 13C NMR spectra: Br HO Br Br O Br O O Br A B C D E 61. 4 signals D 62. 3 signals C 63. 4 signals A 64. 4 signals E 65. 3 signals B Assign the peaks for the following compound in questions 66 ­70 66. 67. 68. 69. 70. 169ppm, choose A ­E for the spectra above (C) (D)C 155ppm, choose A ­E for the spectra above (A) 131ppm, choose A ­E for the spectra above (B) 24ppm, choose A ­E for the spectra above (D) 14ppm, choose A ­E for the spectra above (E) (C) C O H N (B) C C(A) O C(E) Mass Spectrometry Match the following structures to their mass spectra: OH HO O Br O A B C D E 71. C 72. E 73. D 74. A 75. B 76. What is the ratio of M+ to M+1 in a compound with a deuterium atom? a. 1:1 b. 2:1 c. 3:1 d. 99.9:1 e. None of the above 77. Consider the following compound. What would be the possible mass peak upon its McLafferty fragmentation? O a. 43 b. 58 c. 71 d. 85 e. None of the above 78. What is a characteristic fragment mass/charge of a primary alcohol? a. 29 b. 31 c. 43 d. 91 e. None of the above 79. Upon bombardment of a compound with a single electron in the mass spec... a. One electron is lost and a +1 charged compound is formed b. Two electrons are lost and a +1 charged compound is formed c. Two electrons are lost and a +2 charged compound is formed d. One electron is lost and a  ­1 charged compound is formed e. None of the above 80. Which of the following peaks will appear in the mass spectrometry due to a McLafferty rearrangement for the following molecule? O a. 59 b. 77 c. 116 O d. 189 e. 220 81. When a methyl ketone fragments, what type of species is formed? a. Radical anion b. Acylium ion c. Tropylium ion d. Molecular Ion e. None of the above 82. What is the unsaturation number of a compound that exhibits a M+ peak of 94? a. 0 b. 1 c. 2 d. 3 e. 4 83. What is the unsaturation number of a compound that exhibits a M+ peak of 111 and has 1 nitrogen atom? a. 0 b. 1 c. 2 d. 3 e. 4 Combined Spectra Use the combined spectral data to solve the structures for the following problems. The answer choices for the following problems are: O O O O O OH OH O O OH A B C D E 84. Based on the following IR, 1H and 13C NMR spectra, choose the appropriate structure that matches best. D 85. Based on the following IR, 1H and 13C NMR spectra, choose the appropriate structure that matches best. C 86. Based on the following IR, 1H and 13C NMR spectra, choose the appropriate structure that matches best. B 87. Based on the following IR, 1H and 13C NMR spectra, choose the appropriate structure that matches best. A 88. Based on the following IR, 1H and 13C NMR spectra, choose the appropriate structure that matches best. E Equations: N=c/ʋ E=hc/λ P=P°X PTotal=PA+PB Υ=PA/PTotal K = [A]org / [A]aq [A]aq final / [A]aq initial = [(V2/(V2+V1K)]n pKa =  ­log Ka weight % = mass ratio of solute to solution mol % = mol ratio of solute to solution Tables: ...
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