CEM 850 Final Exam H N H H O H H O H C H 2. MeO

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1 CEM 850 Final Exam December 11, 2003 This exam consists of 20 pages. Be sure to write your name on all pages of the exam. Please write legibly and draw all structures clearly. Good luck. 1. (10 pts) Estimate the pka values of the following compounds and write the value in the box below the corresponding compounds: 3 C C 2 Me C 2 2. (3 pts) In the appropriate space show (a) the enol tautomer of A, (b) the keto tautomer of A, and (c) the Z-enolate derived from A. C CF 3 a) A b) c) 1

2 3a. (2 pts) Circle the one cyclic, conjugated molecule possessing 4n + 2p electrons among 1 3 that you predict would display the stability of an aromatic molecule? 3b. (5 pts) BRIEFLY explain why the other two molecules are not aromatic (4 pts) Vitamin E is a powerful antioxidant capable of capturing free radicals that cause cellular damage in living organisms. The synthetic antioxidant BT, commonly found in packaged foods, performs a similar function, preventing development of rancidity. Assuming that the free radical species R would initially abstract a hydrogen atom from the functionalities of these compounds, use the BT framework to draw the four resonance forms that would rationalize the stability of the resulting phenoxyl radicals. BT 2

3 5. Ions 2 + and e 2 + have similar bond strengths (ca. 60 kcal/mol) but neutralization of their positive charges by adding an electron results in bond strengthening for one and dissociation for the other. Label the simple M interaction pictures below (4 pts), and use them to help explain (4 pts) the similarity of the cations and the difference between the neutralized systems. Explanation: 6. (4 pts) Consider the 4 unsaturated molecules below and answer the following questions. Br A B C D (a) Which molecules can be polymerized via a cationic mechanism? (b) Which molecules can be polymerized via a radical mechanism? 3

4 7a. (7 pts) 1,2,3,4,5,6-hexachlorocyclohexane exists as a number of cis-trans isomers. Using the flat cyclohexane stencil and dashed-wedged lines, draw all of them. 7b. (3 pts) ne of the isomers from 7a whose structure is shown below is an insecticide (lindane, gammexane, kwell). Draw the two chair conformations of this isomer and indicate which is more stable. Cl Cl Cl Cl Cl Cl 4

5 8. Joe Clueless, a typical first-year graduate student at Minnesota State University, predicted that an aldehyde was formed as a significant product during reaction of propionyl chloride with benzene: Cl AlCl 3 (a) (5 pts) Provide a detailed mechanism for the formation of the presumed aldehydic product. (b) (5 pts) Do you agree with Joe Clueless that the indicated aldehyde is a significant product formed during the Friedel-Crafts acylation? Provide a BRIEF explanation for your answer. 5

6 9a. (6 pts) Draw the three pi(p) molecular orbitals of an allyl cation, indicating the symmetry of each and the number of electrons in each. 9b (4 pts) Cyclopropyl cations open thermally to allyl cations. Below is an example. Add the methyl groups to the partial product drawing below, being sure to indicate their correct stereochemical positioning. 3 C 3 C D 10. (4 pts) If cyclobutane were flat, it would have exactly 90 C-C-C bond angles and could conceivably use pure p-orbitals in its C C bonds. What would be a possible hybridization for the carbon atoms of the molecule that would allow all of the C bonds to be equivalent? Exactly where would the hydrogens on each carbon be located? 6

7 11a. (3 pts) The reaction below is not concerted but occurs by two consecutive concerted reactions. Complete the drawing of the intermediate species indicated below: Ph C 3 C D C D 3 C Ph C C 11b. (6 pts) Provide a detailed arrow pushing mechanism for the formation of the intermediate species you indicated above. 11b. (5 pts) Explain in writing the stereochemistry of both the intermediate and final products. 7

8 12a. (3 pts) In the following aromatic substitution of indole, gramine (a flavoring constituent of beer) is produced as the major product. Substitution will occur preferentially at only one position of the indole. Provide the product., Ac major product 12b. (3 pts) Consider the related substitution reaction with pyrrole. What is the product formed in this reaction, Ac major product 12c. (5 pts) Explain the observed regioselectivities for the reactions of indole and pyrrole (6a-b). 8

9 13. (8 pts) Provide the structures of A D: Mg(0); the C 2 ; then 3 + / 2 LiAl 4 ; then 3 + / 2 A B (C ) B, DCC, C 2 Cl / 2 TF, heat B + C C D (C ) 14. (2 pts per box) Fill in the boxes, and provide stereochemistry if relevant. C C t-bu 9

10 mcpba major product Me mcpba major stereoisomer 1. 2 Ph MeC 2. 2, 3 + ote: you may ignore the stereochemistry of the product + C 2 1. heat C 2 2. C

11 Cl Cl major product ethylvinylketone a, 2 3 C Me 2 Ph C 3 1. MeI 2. Ag 2, 2 3. heat Ph Me 2 Ph C 3 1. MeI 2. Ag 2, 2 3. heat Ph Me 2 Ph C 3 1. mcpba 2. heat 11

12 Br Br + C 2 (CMe) 2 1. ame 2. +, 2, heat C 2 Et + C aet Et + diethyl malonate ame Me 3 + heat C Ph 3 PCC 3 s 4 as

13 C Ph 3 PCC 2 Et s 4 as 3 Pb(Ac) , + 2. pyrrophosphoric acid heat aet Et C 2 Et Reissert synthesis: C 3 1. ame, Me Me , Pd/C 13

14 Fischer indole synthesis: heat acid C 3 C 3 Strecker synthesis: 1. 2, Me, 4 Cl, 45 C 2. Cl/ 2 valine Cl Darzens condensation: C 2 Et t-buk 15. (6 pts) Draw the isomeric C 5 7 Cl products for the following two reactions. D Cl hu C 3 14

15 16. (5 pts) Propose a synthesis of the following amine from the given ketone and whatever else you need. steps 15

16 17. (5 pts) Design a synthesis to prepare aniline from toluene; you may use any common reagents. 16

17 18. (5 pts) Design a synthesis of 2-benzylcyclopentanone from C-(C 2 ) 4 -C and any reagents of not more than 7 carbons. 17

18 19. (6 pts) Provide a detailed arrow pushing mechanism for the following reaction, being sure to account for formation of a methoxy compound in which the stereochemistry of the oxygen has changed. 1. a 2. Me I Me 18

19 20. (6 pts) Provide a detailed arrow pushing mechanism for the following reaction. C C + dimethylamine + acetone + Me Me 19

20 21. (6 pts) Provide a detailed arrow pushing mechanism for the following reaction that explains the following rearrangement: D Bonus Question: (2 pts) Which former MSU chemistry graduate student served as the Munn ice arena soloist, regularly singing the Stars Spangled Banner prior to MSU hockey games? a. Devi Adhikari b. Thomas Bannon c. Mrunal R. Thatte d. Stephanos Tsirakoglou e. Gang Zuo 20