Chemistry 52 Final Exam. Name: 9 March This exam has six questions, two cover pages, seven exam pages, and two scratch pages.

Transcription

1 Chemistry 52 Final Exam Name: 9 March 2002 This exam has six questions, two cover pages, seven exam pages, and two scratch pages. Please check before beginning to make sure no questions or pages are missing. 120 minutes have been allotted for completion of the exam. All scratch work should be done on the backs of pages or on the attached blank pages. Please put your name on BT cover pages. Make sure that your final answers are clearly indicated and that you clearly cross out any mistakes!!

2 Name: 1. (45) 2. (30) 3. (30) 4. (15) 5. (10) 6. (30) TIPS: Look over the entire exam first! Count carbons and double check your structures! If you get stuck someplace, draw out the structures and start moving electrons or drawing resonance structures. If you really get stuck on a problem, move on and come back to it later. Monster trucks on Channel 19.

3 Predict the major organic product for each set of reactions (eight total) given below. Show intermediate products in the spaces provided and draw your final product in the box. Reaction by-products have not been shown. (5 pts. ea., 45 pts. total) a) Et 1) NaEt/Et 2) Br MCPBA (RC 3 ) b) 1) Na 1) g(ac) 2, 2 2) C 3 Br 2) NaB 4 c) 1) N 3, CN, 2 2) 3 + Et 3 N d) C N 2 N C N (DCC) 1) LiAl 4 2) 2

4 - 2 - e) PCl 3 Ph Ph n equivalents pyridine benzoyl peroxide (1 equ.) n equivalents heat (neglect end-groups) f) C C 2 Wohl Degradation 1) N 2 2) Ac 2 /Ac 3) NaMe N 3, heat g) Et N Et 1) NaEt/Et 2) C 3 Br 3 + heat h) 1) 2) 3 + MgBr, TF Jones' Reagent (Cr 3, 3 +, Acetone) i) 2 NaEt/Et - 2 1) (C 3 ) 2 CuLi 2) 3 +

5 Propose an efficient route for the synthesis of -methyltyrosine from toluene. Use any other reagents you need. Assume that o- and p-isomers can be separated and don t worry about resolving enantiomers. (30 pts.) C 3? N 2 C 3

6 Consider the reaction scheme (the Reissert Indole Synthesis) drawn below. (30 pts.) 1 C 3 N 2 1) Et 2 2) + Et, K Et 3) 2 /Pt, C 3 C N C 2 Et 4 (A) The first step of the reaction involves the deprotonation of the benzylic carbon of o-nitrotoluene (1). For benzylic protons, the typical pk A is approximately 42. Draw resonance structures to show why these protons are acidic enough to be removed by ethoxide anion [pk A (Et) 16] (B) The next step of the Reissert Indole synthesis involves nucleophilic attack of the benzyl anion formed in part (A) on diethyloxalate (2) in a Claisen-like fashion to give product 3 (see part C, next page) upon acid work up. A full stoichiometric equivalent of base is required for formation of the product Draw a detailed mechanism for this reaction and clearly indicate the steps that are essentially irreversible.

7 (continued) (C) In a separate step, the nitro- group in the product formed in part (B) is reduced by catalytic hydrogenation in the presence of acetic acid to give the aromatic amine 3. Acid then catalyzes the formation of the indole derivative 4. (In this case, generation of the aromatic indole ring system favors formation of the enamine-like product rather than the imine-like product.) Show a detailed mechanism for the acid-catalyzed cyclization of 3 to the indole product 4. C 2 N 2 3 C 2 Et 3-2 N C 2 Et 4

8 Rank the following compounds according to the pk A values for dissociation of the underlined protons, from most acidic (lowest pk A ) on the left to least acidic (highest pk A ) on the right. (15 pts.) C 2 Et N A B C D E F G Et MST Acidic LEAST Acidic 5. Consider the electrophilic bromination of 3-thiophenecarboxylic acid: S Br 2 Br S S Br dioxane NT Why does bromination preferentially occur to give 2-bromo-4-thiophenecarboxylic acid? (Think of what you know about electrophilic aromatic substitution reactions of substituted benzene rings.) Give a detailed mechanism including resonance structures. (10 pts.)

9 Consider the series of eight D-aldohexoses shown below and answer the following questions. (30 pts.) C C 2 allose C C 2 glucose C C 2 gulose C C 2 galactose C C 2 altrose C C 2 mannose C C 2 idose C C 2 talose (a) Identify (by name) the following two D-aldohexoses (drawn in their β-pyranose forms): (b) When the Kiliani-Fischer reaction (1. CN, 2. 2 /Pd-BaS 4 ) is applied to D-lyxose, which two D-aldohexoses are formed? C C 2 Lyxose (c) Which pair of D-aldohexoses gives the same aldaric acid upon N 3 oxidation? (d) Which two of the above D-aldohexoses can each be oxidized to aldaric acids that cannot be prepared from any other D- or L- aldohexose? (e) Which two D-aldohexoses do not give optically active products upon reduction with NaB 4? Last page.

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