Unformatted text preview: Chemistry C343/Spring 2009 Exam 2 May 5, 2009 C343 EXAM 2
Printed Name : There are 11 essay questions with a total of 163 points possible. Please look through the entire exam before starting to ensure that the entire exam is included. Do not necessarily proceed linearly. Finish the problems that you know you can answer easily, and then proceed to the problems on which you need to spend more time. TRY TO RELAX! 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Total /150 (163 points possible) 15 points 15 points 15 points 15 points 15 points 15 points 15 points 15 points 15 points 15 points 13 points Page 1 of 13 Chemistry C343/Spring 2009
1A 1 1 H 1.01 3 Li 6.94 11 Na 23.0 19 K 39.1 37 Rb 85.5 55 Cs 133 87 Fr (223) 2A 2 4 Be 9.01 12 Mg 24.3 20 Ca 40.1 38 Sr 87.6 56 Ba 137 88 Ra 226 3B 3 21 Sc 45.0 39 Y 88.9 57 La 139 89 Ac 227 4B 4 22 Ti 47.9 40 Zr 91.2 72 Hf 178 104 Rf (261) 5B 5 23 V 50.9 41 Nb 92.9 73 Ta 181 105 Ha (262) 6B 6 24 Cr 52.0 42 Mo 95.9 74 W 184 106 Unh (263) 7B 7 25 Mn 54.9 43 Tc (98) 75 Re 186 107 Uns (262) 8 26 Fe 55.8 44 Ru 101 76 Os 190 108 Uno (265) Exam 2
3A 13 5 B 10.8 10 28 Ni 58.7 46 Pd 106 78 Pt 195 1B 11 29 Cu 63.5 47 Ag 108 79 Au 197 2B 12 30 Zn 65.4 48 Cd 112 80 Hg 201 13 Al 27.0 31 Ga 69.7 49 In 115 81 Tl 204 4A 14 6 C 12.0 14 Si 28.1 32 Ge 72.6 50 Sn 119 82 Pb 207 5A 15 7 N 14.0 15 P 31.0 33 As 74.9 51 Sb 122 83 Bi 209 6A 16 8 O 16.0 16 S 32.1 34 Se 79.0 52 Te 128 84 Po (209) 7A 17 9 F 19.0 17 Cl 35.4 35 Br 79.9 53 I 127 85 At (210) May 5, 2009
8A 18 2 He 4.00 10 Ne 20.2 18 Ar 39.9 36 Kr 83.8 54 Xe 131 86 Rn (222) 8B 9 27 Co 58.9 45 Rh 103 77 Ir 192 109 Une (266) Lanthanides Actinides 58 Ce 140 90 Th 232 59 Pr 141 91 Pa 231 60 Nd 144 92 U 238 61 Pm (145) 93 Np (237) 62 Sm 150 94 Pu (244) 63 Eu 152 95 Am (243) 64 Gd 157 96 Cm (247) 65 Tb 159 97 Bk (247) 66 Dy 162 98 Cf (251) 67 Ho 165 99 Es (252) 68 Er 167 100 Fm (257) 69 Tm 169 101 Md (258) 70 Yb 173 102 No (259) 71 Lu 175 103 Lr (260) Page 2 of 13 Chemistry C343/Spring 2009 1 a. Oxidation is a ubiquitous reaction in organic chemistry and as such we felt it was necessary to include it in our laboratory curriculum. Among oxidants, nitric acid is dangerous, and salts of manganese or chromium are environmentally harmful and often messy; therefore, we sought other oxidizing agents devoid of these drawbacks and commercial bleach seemed appropriate as it is a ‘green’ reagent. How would you effectively explain green chemistry to a non‐scientist? (4 points) b. Camphor is a bicyclic compound widely distributed in nature, especially in trees of the Far East. It is used as a plasticizer for the production of celluloid film, for smokeless powders and explosives, as an insect repellent, and for medicinal purposes (e.g. it’s the characteristic odor of Vicks Vaporub). Provide the reagents used in the experiment in the oxidation reaction with bleach and then provide the expected (5 points) product from this reaction below. Exam 2 May 5, 2009 c. What was the active species in the reaction above when the two reagents are added together? (2 points) d. What was the point of employing the starch‐KI test paper in the oxidation reaction? (4 points) Page 3 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 2. Last Saturday night, you snuck into the organic lab because you wanted to run one last base‐promoted elimination reaction since you did not believe the GC results you obtained in lab a few weeks ago (ok, just play along with me). You run the reaction below, and your GC results reveal you obtained a ratio of A:B of 24:76. Provide correct structures for molecules A and B in the boxes. However, you decided that the GC results were not definitive enough, and you run your first 1H NMR experiment by yourself (wow, you truly have come far!). In the space below, sketch molecules A and B, assigning all the signals you observed in their spectra. Indicate the expected integration and splitting pattern as we have done in the past, but this time add in an approximate ppm range where you would expect to see these signals; [2H, t, 1.5 ppm] is enough for simple species. For the more complex splitting patterns, like doublets of doublets, etc., draw out these signals with approximate coupling constants to show what one might expect (like you did on quiz 3). (15 points) b. Provide an example of a suitable NMR solvent you could have used: Page 4 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 3. a. In the reaction acid‐catalyzed hydration of norbornene, you isolated your product from an ether solution, but first you washed it. What was the purpose of washing the ethereal solution of product with sodium bicarbonate solution? (3 points) b. Draw in all the different types of protons on norbornene below that would show up differently in the 1H NMR. Identify them as different by drawing them in as Ha, Hb, Hc, etc, and then indicate how many of each of those protons there are by writing 1H, 2H, 3H, etc., as appropriate. Splitting is not necessary here. (3 points) c. Before you started your Diels‐Alder reaction, you had to ‘crack’ the 1,3‐cyclopentadiene (Cp). Explain what cracking means in 1‐2 sentences. (3 points) d. Choose the best diene and best dienophile from below to demonstrate a Diels‐Alder mechanism and its expected products. Label your products as either exo or endo, and circle the favored product. Suggest in one sentence how can be separated from each other. (6 points) Page 5 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 4. a. You synthesized benzocaine (ethyl p‐aminobenzoate) using Fischer esterification. In the same way, you could have synthesized esters with fruit scents like raspberry, banana, pear, or orange. Provide the correct starting materials and reagent(s) to prepare ethyl butanoate. (3 points) b. Since every step in the above synthesis is reversible, what two, simple things can you do to shift the equilibrium toward products? (You actually did one of these in your reaction to make benzocaine.) (2 pts) c. When you prepared and recrystallized PABA, you obtain an IR spectrum. If you saw a broad stretch at 3300 cm‐1, what two things could this indicate to you? (3 points) d. For each structure, determine how many carbon signals that would be observed in the 1H NMR. (7 points) O H3CO N O O OCH3 OCH3 HO O OH O O O O O H3CO O OH O Page 6 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 5. a. Why did you need to use anhydrous diethyl ether as your solvent for the Grignard reaction? What is the consequence of not using anhydrous ether? (3 points) b. Acetone is not a suitable solvent for a Grignard reaction; why? Why does anhydrous diethyl ether not have this same problem? Write out a balanced reaction of your Grignard reagent with acetone. (4 points) c. During the Grignard reaction, your AI told you to add a small amount (ca. 5 mL) of anhydrous ether to your reaction set‐up and let it evaporate out the top while you were getting everything ready. What was the purpose of this step? (2 points) d. A Grignard reaction can be used to prepare Benadryl. Show the steps (i.e. in order to assign partial credit) and final structure of Benadryl below. (6 points) Page 7 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 6. a. You tested the reactivity of electrophilic aromatic substitution with bromobenzene with HNO3/H2SO4 to give the o‐ and p‐substituted products. Give two good, obvious reasons why it would have been impractical to brominate nitrobenzene to get these identical products. (4 points) b. Draw the three most likely mono‐chlorination products for the aromatic compound below, putting them in order of their expected product distribution. (3 points) c. You decided to try your new skills of nitration on other substrates, so you add HNO3/H2SO4 to aniline expecting to obtain the same substitution products you did obtained with bromobenzene. Briefly explain why you get these unexpected results, after workup with sodium bicarbonate. Remember from your reaction that the acid is in excess and the aniline is the limiting reagent. (3 points) NH2 HNO3/H2SO4 NH2 NO2 d. You separated o‐nitrobromobenzene (yellow solid) from p‐nitrobromobenzene (white solid), using recrystallization. What allowed you to separate these from each other using this technique? If you were to have separated them by column chromatography what compound would elute first if you to use 10:1 petroleum ether: ethyl acetate as your solvent. Why? (5 points) Page 8 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 7. Below are two mass spectra for three possible isomers for the formula, C8H8O2, weighing 136.2 amu. Identify which mass spectra are for which compounds and give brief reasons why, i.e. provide structures for ions that relate to the major numbered peaks that led you to your decision definitively. Be persuasive for full points. Lastly, what one major fragmentation pattern would you have expected for the isomer whose spectrum is not below? (15 points) Compound: Compound: Page 9 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 8. Determine the structure for the following compound, C11H20O4, based on the given data. (Only a circled, clearly drawn final answer will be graded for credit. Scribble will be ignored.) Label your final drawing with a, b, c, etc., as appropriate and then label the proton NMR with the corresponding signals. (15 points) • MS data showed the following peaks: M‐15, M‐45, M‐57, and M‐73. • IR data shows peaks at 3080‐2900 and 1740cm‐1. 180 160 140 120 100 PPM 80 60 40 20 0 (There are two peaks almost overlapping at 27.7 and 28.4 ppm.) Page 10 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 9. Determine the structure for the following compound, C11H14O2NX, based on the following data provided. (Only a circled, clearly drawn final answer will be graded for credit. Scribble will be ignored.) Label your final drawing with a, b, c, etc., as appropriate and then label the proton NMR with the corresponding signals. (15 points) • MS data showed the following peaks: 1:1, M+:M+2 peak, M‐16, M‐73, M‐79. • IR data shows peaks at 3300 (two sharper peaks), 3080‐2900, 1740, 1600, and 650 cm‐1. Page 11 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 10. Short answers. (notice the word ‘short’) (15 points total) a. What is the approximate sample size in order to obtain a mass spectrum? (1 point) b. What two things must happen to the sample in order for it to be analyzed in the spectrometer? (4 points) c. How are the fragments separated by mass in the spectrometer? (3 points) d. What is responsible for the M+1 peak that is always present in organic samples? (2 points) O e. Demonstrate drawing the arrows for a McLafferty rearrangement on 2‐hexanone, providing correct final products. (3 points) f. CO2 has a mass of 43.9898 amu while N2O is 44.0011 amu. What MS technique would you need to use to differentiate between these two molecules? (2 points) Page 12 of 13 Chemistry C343/Spring 2009 Exam 2 May 5, 2009 11. You know that alcohol protons resonate at 2‐4 ppm, whereas vinyl alcohols can have resonances as down field as 16 ppm. The nitrogen protons on a primary amine such as n‐butyl amine show up in the 1H NMR at ca. 5 ppm. However, the protons on a primary amide, such as butyramide, resonate around 8.0 ppm. Briefly explain this huge disparity in resonance of nitrogen protons. (5 points) b. When we did some problems in class, it was obvious that you could not tell some isomers apart very easily. However, these two isomers below can be differentiated quite easily. How would the 1H NMR spectrum of ethyl 4‐aminobenzoate differ from the 1H NMR spectrum for 4‐(dimethylamino)benzoic acid? In addition to changes in the chemical shifts of various peaks, don’t forget to describe any differences in splitting and integration as well. (8 points) Page 13 of 13 ...
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