CHEM 231 (Davis) Organic Chemistry Exam III 19 April, YOUR NAME (Last, First, M.I.) DISCUSSION SECTION #53 (5 Points)

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1 EM 23 (avis) rganic hemistry Exam III 9 pril, 2006 YUR NME (Last, First, M.I.) ISUSSIN SETIN #53 (5 Points) Initial of last name Instructions Please fill in your name in the space above and on the next page Please put your discussion section number in the space provided. Print the initial of your last name in the box above Please sign your name under the onor ode acknowledgment on the following page

2 Name EM 23 Exam III 9 pril, 2006 This exam is worth 200 points Notes The exam period is 50 minutes. t the end of 50 minutes, all exams will be collected in a timely fashion; there will be no exceptions University onor ode cknowledgment I certify that I have neither given nor received assistance of any kind in the completion of this examination. Signature Points iscussion Section (5) Problem (30) Problem 2 (40) Problem 3 (50) Problem 4 (35) Problem 5 (20) Problem 6 ( 20) Total (200) EXM EGINS N NEXT PGE 2

3 . a) (5 points) For the transformation below, provide a detailed arrow pushing mechanism ,2 ydride Shift b) (5 points) For the transformation below, provide a detailed arrow pushing mechanism. Problem l l 3 3 l 3 3 3,2-alkyl shift l l 3

4 2. (40 points) For each of the reactions below, provide the reagents that are needed to obtain the indicated reaction products. Write the necessary reagents above the reaction arrow. You may use any chemical reagents as needed, including the following: 3, 2, 2 0, g(c) 2, Na 4, I 4, s 4, NaS 3, l 3, tuna,diazomethane,ns, 2, Pd/, Me, I 2, 2 S 4 Example: 2, Pd/ 2 S 4 2 ) s 4 2) NaS 3 ) 3 2) Me 2 S l 3 K l l 2, 2 4

5 3. (50 pts). Short nswer. a. The structure below has 2 additional resonance structures; draw them. raw arrows to indicate the flow of electrons between resonance structures. lso, make sure you draw the correct arrows indicating that the structures are resonance forms (20 points) b. Roadmap. Supply missing reagents and structures within the boxes (20 points). Note that p-tsl turns alcohols into alkyl halides ) 3 2) 2 2 p-tsl l 3 3 Pyridine 3 ) NaN 2 2) 3 -I _ Na , Lindlar catalyst N

6 c. There is something wrong with the following figure. iefly explain the problem and draw a more accurate figure (0 pts). ddition of water to bromonium ion occurs via Markovnikov addition to the more substituted carbon. 4. (35 points) etermine the stereochemical configuration (R/S) of the chiral center (*) for each of the molecules below. Place your answer in the space below each drawing. F 3 l * 3 * 3 2 N 3 3 * 2 3 F * S S R S S 6

7 7 5. (20 pts). zone adds to alkenes to give an ozonide. Two general mechanisms for this reaction can be envisioned. In the first mechanism (the actual one) ozone adds in a single step to give the ozonide directly. In the second mechanism ozone might add to the alkene in 2 steps with an intermediate intervening between starting material and product. a) raw careful, detailed arrow formalisms for both mechanisms. You will need a good Lewis dot structure for ozone. 3 _ Mechanism -oncerted-ne Step process Mechanism 2-Stepwise-Two Step process with an intermediate

8 b) evise an experimental test that would distinguish the -step and the 2-step mechanisms for ozonolysis of an alkene. e specific-what is the structure of the alkene that you would use and what is the structure of the product that you would obtain? If concerted mechanism the reaction should be stereospecific. this is alken should give cis ozonide If 2 step mechanism with carbocation intermediate the reaction should be stereospecific. is alkene might give mixture of cis and trans ozonides, as one can rotate about - sigma bond in the intermediate. 3 3 _ 3 3 _ IS TRNS 8

9 6 (20 pts) The ammond postulate indicates that the free energy of activation (dg ) for the pathway to form a 3 o carbocation is lower than that to form a 2 o carbocation. For the following reaction draw the energy levels of the carbocation intermediates and respective transition states, including the respective dg,so that the diagram is consistent with ammond s postulate. Let s assume that the reaction is exergonic and that the energy of the products compounds 2 and 3 are identical. 3-2 major 3 3 minor 3 3 Free Energy G # 3 G # 3 - Starting materials 3 minor major Minor Rxn Progress Major 9

10 NTING N TIS SEET F PPER WILL E GRE 0