Organic Chemistry Final Exam (Chemistry 220a) - December 19, 2001, Exams of Organic Chemistry

Download Organic Chemistry Final Exam (Chemistry 220a) - December 19, 2001 and more Exams Organic Chemistry in PDF only on Docsity! FINAL EXAM Organic Chemistry Chemistry 220a; 2 P.M., Wednesday, December 19, 2001 NAME (print): ______________________________________________________________ TA:_____________________ Section Day:_____________ Section Time:______________ Take a few moments to look over the exam. Do problems first with which you are most comfortable. Important points and unknowns a bold type. Do all preliminary work on the worksheets. The worksheets will not be graded. The following tables are at the end of the ex Periodic Table (page 21), BDEs (page 22), Common Isotopes (pg. 23). The exam is 2 to 2-1/2 hours with an additional 1/2 hour for revi STOP writing when you are asked to do so. Put your name on the cover sheet and subsequent pages where indicated. For questions 2 and 4, you are to complete only one of the two choices that are offered for each. For question 3, do 4 of 6. See directions on the exam. For question 5, do 1 of 4. For question 6, do 4 of 6. For question 8, do 5 of 6. R :EMEMBER Neatness is to your advantage. Have a GREAT winter break! See you next term for Chem 221b. 1. Naproxen (36 pts) ________ 5. Mechanism (20 pts.) _________ Revisited 2. Structure (30 pts) _________ 6. Kinetics/ (32 pts.) _________ Thermodynamics 3. Potpourri (40 pts) _________ 7. Radicals (32 pts.) _________ 4. Synthesis (30 pts) _________ 8. Reactions (30 pts.) _________ ______________________________________________________________________ Total (250 pts) ______________ 1. )-(+)- Naproxen ( )-(+)-Naproxen is by catalytic hydrogenation of carboxylic acid N a p r o x e n Revisited: (6 x 6 pts. = 36 pts.) In exam 2, we considered the resolution of racemic Naproxen to isolate (S A). The current method for preparing ( S B . a) Is B chiral or achiral? Why? 4/17/02 11:10 AMFinal-01 Page 1 of 10file:///Macintosh%20HD/Users/fziegler/WEBSITESFOLDER/Chemistry220a/studyaids/oldexams/exams-F01/Final-01.htm b) Will hydrogenation of )-(+)-Naproxen efficiently (>75%)? Explain briefly. B in the presence of a noble metal such as Pt form (S c) The optically active rhodium catalyst C, Rh(DIOP)Cl , which was used in your text (pg. 219) to illustrate asymmetric hydrogenatio [2001 Nobel Prize in Chemistry], might be an ideal catalyst to produce only a single enantiomer of Naproxen. 2 Briefly illustrate an explain the principle of asymmetric hydrogenation in general terms. [Hint: Recall how you were to illustrate the resolution of Nap in exam 2.] d) What are the configurations (R/S) of the stereocenters present in the ligand D used in the formation of catalyst C? Label them below. e) The four carbon chain of the ligand D above is derived from one of the stereoisomers of tartaric acid. Which one is it? Draw it in a Fischer projection. [Hint: see below] 4/17/02 11:10 AMFinal-01 Page 2 of 10file:///Macintosh%20HD/Users/fziegler/WEBSITESFOLDER/Chemistry220a/studyaids/oldexams/exams-F01/Final-01.htm c) The indole alkaloid quebrachamine ( ] = -110 . An attempted resolution of (±)- ] = -33 . What percentage of the 1) has a specific rotation [α D o 1 led to a sample that had [α D o dextrorotatory enantiomer was present? Show work. d) The peracid epoxidation of (E)-2-butene (zero inversions) is the operational equivalent of what two inversion process? Illustrate and explain briefly. e) What is one property that the compounds acetylene, hydrogen cyanide, and BeCl share in common? Explain 2 briefly. f) Arrange (left to right) the following carbocations in increasing order of stability: (CH ) C (t-butyl cation), (CH ) CH (2-propyl cation), and CH OC(CH ) (2-methoxy-2-propyl cation). Explain 3 3 + 3 2 + 3 3 2 briefly. Do only 4a or 4b, not both of them! 4a. Synthesis: (30 pts.) A chemist requires a sample of 2,5-dimethyl-2-hexanol ( 1, C H O). She recognizes an element of symmetry (C + in the hydrocarbon structure of the alcohol. She designs and executes a synthesis of 8 18 4 C )4 1 from acetone and methanol. She has all reagents and solvents available to her as do you. How would you complete the synthesis of this alcohol under the restrictions indicated? 4/17/02 11:10 AMFinal-01 Page 5 of 10file:///Macintosh%20HD/Users/fziegler/WEBSITESFOLDER/Chemistry220a/studyaids/oldexams/exams-F01/Final-01.htm Place an "X" here if you want 4a graded. ______ Do only 4a or 4b, not both of them! 4b. Synthesis: (30 pts.) A chemist isolates an optically active compound from nature which he believes to be (Z)-3-methyl-4-heptene-3- ol ( 1, C H O). He synthesizes 8 16 1 from 2-butyne as his only source of carbon. All reagents and solvents are available to you as they were to him. Reconstruct his synthesis. Place an "X" here if you want 4b graded. ______ Is the synthetic alcohol optically active? 5. Justify. Mechanism: (20 pts.) Provide the mechanism of one , and only one, of the following reactions. Use the curved arrow formalism. The Na/NH reduction of 2-butyne3 The ozonolysis/dimethyl sulfide reduction of (E)-2-butene The hydroboration/oxidation of (E)-3-methyl-2-pentene The reaction of HBr in the presence of a peroxide with 2-methyl-2-butene 6. Kinetics/Thermodynamics: (4 x 8 pts. = 32 pts.) Do 4, and only 4, of the following 6 problems. If you manage to do 5 or 6 problems, cross out the one(s) that you do not want graded. If structures are shown, circle the correct answer and provide a few words of justification. If no structure is shown, give a brief explanation. 4/17/02 11:10 AMFinal-01 Page 6 of 10file:///Macintosh%20HD/Users/fziegler/WEBSITESFOLDER/Chemistry220a/studyaids/oldexams/exams-F01/Final-01.htm a) The compound with the lower rate for E2 elimination. Justify. b) The compound with the greater rate of E2 elimination. Justify. c) Of (Z)-2-butene and (E)-butene, the one with the greater heat of hydrogenation. Illustrate and justify. d) The compound that gives the higher ratio (S 2/E2) of S 2 to E2 product when reacted with KOH. N N Justify. e) The heat of hydrogenation of ethylene to ethane is -32.9 kcal/mol and the heat of hydrogenation of acetylene to ethane is -74.5 kcal/mol. 4/17/02 11:10 AMFinal-01 Page 7 of 10file:///Macintosh%20HD/Users/fziegler/WEBSITESFOLDER/Chemistry220a/studyaids/oldexams/exams-F01/Final-01.htm