Chemistry 216 Second Examination Name___KEY___________ December 9, 2008 Please print Professor Masato Koreeda (2 hrs, 120 points) Signature _______________________ Student ID # _____________________ Please CHECK OFF your lab section. High: 118/120; Median: 76/120 (63.3%)216 F08 Exam #2: Name _____Key______________ Page 2. I. (10 points) Draw the structures for the organic products containing an ethyl group (CH3CH2) which are expected upon treatment of each of the following chemicals with CH3CH2MgBr, followed by acidic work-up. Note that acetone is (CH3)2C=O. (1) D2O (3) acetone(2) dry ice (CO2)(4) propanoic acid [CH3CH2C(=O)OH]+H3C CHHDH3CCCOOHHHH3CCCCH3HHOHCH3H3C CH3H3CCCOOHHH 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 BrC6H5). 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. Br+ MgMgBrHOH+MgBrHO 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. (1) (2 points) What is brine? saturated aqueousNaCl solution (2) (3 points) What is the purpose of this washing with brine? To reduce the amount ofwater dissolved in theorganic layer. (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. MgSO4 + 7 H2O -> MgSO4•7H2O216 F08 Exam #2: Name______Key____________ 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. 4Ph3P+_O+O4PhPhOONaOCH3HOCH3+Ph3P=O(1)(2)6Mechanism:6Mechanism:OOPOPhPhPhOPPhPhPhHOO+Ph3P=Omech: 2 ptsstr: 2 ptsmech: 2 ptsH3COPhOHOPhH3COPhOHOPhH3COPhOOPhPhPhOOOCH3PhPhOH3COOHOCH3mech: 2 ptsstr: 2 ptsmech: 2 pts216 F08 Exam #2: Name______Key____________ Page 4. V. (4 points). The proton NMR spectrum of a mixture of acetone [(CH3)2C=O], p-dioxane (C4H8O2), and dichloromethane (CH2Cl2), is integrated and results in step heights of 18, 12, and 2 mm for the signals at δ 2.17, 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. No 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. acetone : p-dioxane : dichloromethane =18/6 : 12/8 : 2/2 = 3 : 1.5 : 16 : 3 : 2 VI. (12 points). For each of the reactions given below, draw in the box the structure of the expected organic major product. Make sure to indicate the stereochemistry of the product whenever applicable. 3endo product+room temperatureCH2Cl2(solvent)PhPhOOO(1)OOOPhPhHHHHOOOPhPhHHHHorcorrectconnectivity: 2 pts (2) +90 °Cbenzene(solvent)NBocOOOCH3H3COnote: Boc =OO CH3CH3CH33 3+product A (racemate)product B (racemate)correctconnectivity: 2 ptsNBocHHOOCH3HOOCH3NBocHHOOCH3HOOCH3Without this stereochemical indication, structures do not constitute accetable answers.There is no endo/exo issue here! Which of the two racemic products A and B would you expect to be predominant in this reaction? Explain your answer. The predominant product should be: __A___Explanation for your answer:3NHHHOOOCH3H3COBocBstericrepulsionIn the transition state that leads to product B, there should exist a serioussteric repulsion between the methyl estergroup and the ring methylene groups of the ring of the diene.Note: It is not the steric interactioninvolving the Boc group that matters.216 F08 Exam #2: Name ________Key_______________ Page 5. VII. (10 points) On the basis of the spectroscopic information given, assign the structure to compound C, C6H10O. Compound C IR (liquid film): strong absorptions at 1692 and 1621 cm-1; no peaks in the 4000-3200 cm-1 region 1H-NMR (CDCl3) δ 1.89 (3H, singlet), 2.14 (3H, singlet), 2.22 (3H, singlet), and 6.09 (1H, singlet). 13C NMR (CDC3) δ 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 an O-containing functional group in this compound? Ketone or α,β−unsaturated ketone__ (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. 5H3CCH3OH3CH 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 NH2HNO2NH2NO2HHNH2HHNO2HHHHHHH9876432165510216 F08 Exam #2: Name ________Key________________ Page 6. IX. (12 points) The following three 1H NMR spectra (at 300 MHz in CDCl3) are of isomeric mono-substituted aromatic esters with formula C10H12O2. Draw in the boxes provided the structures of the compounds. No explanation needed. No partial credit will be given
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