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216%20F08-E2-key - 216 F08 Exam#2 Name t6 I(10 points Draw...

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Unformatted text preview: 216 F08 Exam #2: Name t6 I. (10 points) Draw the structures forth are expected upon treatment of each of the o owing chemicals with CH3CH2Mg r, o owed by acidic work—up. Note that acetone is (CH3)2C=O. (1) D20 (2) dry ice (C02) (3) acetone . (4) propanoi acid [CH3CH2C(=O)OH] II ( 4 points). The Grignard reaction has to be carried out under anhydrous conditions. Explain what would happen to the Grignard reagent formed from bromobenzene (BrC6H5) and Mg if the solvent ether used for the reaction is contaminated with a small amount of water (i.e., more than one equivalent to the BrCGHs). Show the structure of the Grignard reagent to be formed from BrC6H5 and Mg and provide a chemical mechanism using the curved—arrow convention as to what effect the water can have to the Grignard reagent. ,1) Bymj ._. @[Mjfr —-> {D + Hot/ya H~0H . III (8 points). In a number of experiments you performed in the lab, the product mixtures were extracted with diethyl ether or dichloromethane a few times. The combined organic layers were first washed with water and then with brine. The resulting organic solution then was dried over a drying agent such as anhydrous calcium chloride, sodium sulfate, and magnesium sulfate. Answer in the box provided the following questions. 3 ,I J” ,. ’cl 14$ (1)(2 points) What is brine? NM 06 $0 [m (2) (3 points) What is the purpose of this washing with .75 2’5 dzl/t Cé’, J71}? [z "10% ,, 97L brine? , - x war? rd135c3/t/6d L m (3) (3 points) What is the chemical basis for the use of an anhydrous drying agent? Explain using magnesium sulfate as the example. Be specific if any chemical process is involved. M3554, ’f' 7/720 ‘———$ MfSWc/J 7/220 216 F08 Exam #2: Name I: 62 Page 3. IV (20 points). For each of the reactions given below, draw in the box provided the structure of the expected major reaction product and propose a reasonable step—by—step mechanism for its formation using the curved—arrow convention. (1) o I p o + Ph3P+\/“\ Mechanism: 216 F08 Exam #2: Name £ 3 Z Page 4. V. (4 points). The proton NMR spectrum of a mixture of acetone [(CH3)2C=O], p—dioxane (C4H802), and dichloromethane (CHZCIZ), is integrated and results in step heights of 18, 12, and 2 mm for the signals at 62.17, 3.50, and 5.20 ppm, respectively. In what mole ratio are these three substances present? Provide your answer in the box shown below. No explanation required. N 0 partial credit will be given to this problem. Please note that the chemical shifts of acetone, p-dioxane, and dichloromethane are, respectively, 2.17, 3.50, and 5.20 ppm. 3 : l, 9 : l _ acitégne :p-di/OEane :dichlgoromethane = WC? / : —/ ~ ~’ owned?” 6 5“ Z 74213 . VI. (12 points). For each of the reactions given below, draw in the box the struct e of the expected organic major product. Make sure to indicate the stereochemistry of the product wh never applicable. (1) 0 room PhWPh + l 0 temperature CH2Cl2 O (solvent) endo product PM (2) Wécf’miwcfi‘wg, 4 an 0 $00 N \ O OCH3 / benzene (solvent) H3CO O 0 CH3 — product A (r cemate) m {‘5 M wrote 45x0 255% Which of the two racemic products A and B would you expect to be predominant in this reaction? he“ Explain your answer. The predominant product should be: Explanantion for your answer: IV] W t1®449rriW ' HMS/wafcl ha a $6er W; _ C fifemz VZ/fl/Jf/W btfw” \ B Mama of m dram 1149 not W sale/n 2717‘: M Void, W ' 80am» 216 F08 Exam #2: Name K62 Page 5. VII. '(10 points) On the basis of the spectroscopic information given, assign the structure to compound C, C6HIOO- Compound C IR (liquid film): strong absorptions at 1692 and 1621 cm}; no peaks in the 4000—3200 cm‘1 region lH—NMR (CDCla) 6 1.89 (3H, singlet), 2.14 (3H, singlet), 2.22 (3H, singlet), and 6.09 (1H, singlet). 13C NMR (CDQ) 6 20.57, 27.55, 31.58, 124.30, 154.8, and 198.35 ppm (1) (1 point) What is (are) the unit(s) of unsaturation of this compound? 2 (2) (2 points) What do the IR and 13C NMR spectra tell you in terms of the presence of the O-containing functional group in this compound? K8 W WO/ mi: .1 (3) (2 points) How many alkenic carbon peaks are there in the 13C spectrum? 2— (4) (5 points) Draw the structure of this compound in the box below. VIII. (12 points) Shown below are the 1H NMR spectra (only the aromatic H regions shown) of three regio isomers of nitroaniline. Make assignments of all aromatic hydrogens by writing peak numbers on the spectra in the box near each of these hydrogens. Please note that the NMR spectra are not given in any specific order. 216 F08 Exam #2: Name, K6 2 Page 6. IX. (12 points) The following three 1H NMR spectra (at 300 MHz in CDC13) are of isomeric mono— substituted aromatic esters with formula C10H1202. Draw in the boxes provided the structures of the compounds. No explanation needed. No partial credit will be given to this problem. 216 F08 Exam #2: Name Q: >1 Page 7. X. (16 points) On the basis of its spectroscopic information provided below, propose the structure of the compound C9H1604). Draw the proposed structure in the box below and give in the box on page 8 a brief expla tion by assigning the IR 1745 cm'1 peak and all 1H and 13C NMR peaks. 2 “mi; of amusing/WM IR: strong absorptions at 1745 cm]; no absorptions between 4,000—3,000 cm‘l. ester? M W ZOMHz carbon—13 NMR spectrum CDCl3 solution proton decoupled 100MHz proton NMR spectrum CDC}.3 solution ‘m m 3.2 It? [,3 N PM PM (7;. W 216 F08 Exam #2: Name K6 Z Page 8. X. (continued) IR, NMR assignments: XI. (12 points). Show how many peaks you would expect to observe in the proton—decoupled 13C NMR spectra of the following compounds. Indicate your answers in the box provided. Do not count the 13C NMR peaks of the solvent and TMS. (“J/LI rcl/QCH miter” ) O o: GE cm O r (at room 2 l ...
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