CHEM 203. Final Exam December 12, This a closed-notes, closed-book exam. You may use your set of molecular models. This test contains 11 pages

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1 CEM 203 Final Exam December 12, 2012 Your name: This a closed-notes, closed-book exam You may use your set of molecular models This test contains 11 pages Time: 2h 30 min 1. / / / / / / / / 40 TTAL / 250 = / 100 This exam counts for 50% of the lecture component of your CEM 203 grade

2 Chem 203 final exam p. 2 of (20 pts.) Indicate the approximate pka for the dissociation of the protons in boldface in the following molecules (write your answers in the appropriate boxes): -N 2 C 3 -C 2 C 3 2 Cl 2 (24 pts) Check the appropriate box to indicate whether the procedures below constitute satisfactory or poor methods for the preparation of the compounds shown: a. C 3 1. B 3, then 2 2 and aq. Na 2. TsCl, pyridine 3. C 3 SNa SC 3 C 3 satisfactory poor b. 1. Jones reagent 2. Na 3. Br c. 1. Br 2. NaN 3 3. Zn / + N 2 d. 1. 2, Lindlar cat. 2. 3, then Zn / + 3. C 3 MgBr, then mild 3 +

3 Chem 203 final exam p. 3 of (26 pts) An unknown disaccharide, A, reacted with dilute aqueous 2 S 4 to furnish only compound B (diagram below). The reaction of A with excess C 3 I and Ag 2 afforded compound C. Independent evidence showed that C had the β-configuration at all anomeric positions. The reaction of C with dilute aqueous 2 S 4 produced substances D and E. Deduce the structure of A - C and write your answers in the appropriate boxes. B aq. 2 S 4 A C 3 I Ag 2 C aq. 2 S 4 C 3 C 3 D C 3 C 3 + C 3 C 3 E C 3 structure of disaccharide A structure of compound B structure of compound C

4 Chem 203 final exam p. 4 of (30 pts) Draw: a. A cyclic alkene that furnishes only the product shown below upon reaction with 3 followed by 2 2 and + : C b. An alkyl halide that is likely to react with C 3 Na to give a product of substitution, and one that is likely to react with C 3 Na to give a product of elimination: undergoes substitution undergoes elimination c. An alkene containing at least 3 carbon atoms that will produce the same diol when treated either with s 4 followed by aqueous NaS 3, or with MCPBA followed by aqueous 2 S 4 : d. The Schiff base obtained upon reaction of the compounds shown below in the presence of catalytic + : and N 2

5 Chem 203 final exam p. 5 of 11 e. Fischer projections of a generic D-aldopentose and of a generic L-aldotetrose: D-aldopentose L-aldotetrose f. A carbocation that is stabilized by three hyperconjugative interactions with C bonds and that is likely to rearrange to a new carbocation stabilized by seven hyperconjugative interactions with C bonds: g. A carbonyl compound that furnishes the products shown below when treated with excess C 3 MgBr followed by excess Br structure of the carbonyl cpd. 1. excess C 3 MgBr 2. excess Br Br + Br h. The product of E2 reaction of the substance obtained upon addition of Cl 2 to the alkene shown below:

6 Chem 203 final exam p. 6 of 11 i. An alcohol that upon reaction with Br is likely to undergo conversion into an alkyl bromide by the S N 2 mechanism, and one that that upon reaction with Br is likely to undergo conversion into an alkyl bromide by the S N 1 mechanism: likely to react by S N 2 likely to react by S N 1 j. A trans-alkene that gives a chiral diol upon reaction with either s 4 followed by aqueous NaS 3, or with MCPBA followed by aqueous 2 S 4 : 5. (30 pts) Write accurate mechanisms for the following known reactions: a. C 3 S rad. initiator heat SC 3

7 Chem 203 final exam p. 7 of 11 b. aq. 2 S 4 + c. S Na N=N=N N N N

8 Chem 203 final exam p. 8 of (40 pts.) Draw the structure of the major product expected from the following reactions (write your answer in the boxes). If no overall change is predicted, answer "N REACTIN." a. C 1. LiAl 4, then mild TsCl, pyridine 3. K 1. Na, N 3 (liq) 2. Br 2, 2 b. 3. Na 4. (C 3 ) 2 N c S 4, 160 C 2. MCPBA 3. then mild 3 + Na d / + 3. excess C 3 MgBr 4. mild 3 + e. 1. NBS, rad. init. 2. Mg 3. C 2, then mild 3 +

9 Chem 203 final exam p. 9 of (40 pts.) Indicate all the reagents, catalysts, etc., in the correct order, that are necessary to induce the transformations shown below. List such reagents above / below the reaction arrows. NTE: aqueous workups are understood and do not need to be shown. a. b. c. C d. e. f. N 2 g. h. N 2

10 Chem 203 final exam p. 10 of (40 pts.) Propose a good synthesis of the molecules shown below using only methanol, acetylene and ethylene oxide (see below) as the sources of carbon atoms. Intermediates / products obtained during an earlier sequence may be employed in a subsequent procedure. Assume the availability of all necessary reagents (such as bases, acids, B 3, Mg, TsCl, PCC, PBr 3, MCPBA, etc.). methanol: C 3 acetylene: C C ethylene oxide: 2 C C 2 Important: i. Aqueous workups at the end of each reaction are understood and need not to be shown. ii. It is not necessary to write mechanisms. a. b. C

11 Chem 203 final exam p. 11 of 11 c. d. N 2 appy olidays!