CHEM 203. Final Exam December 16, This a closed-notes, closed-book exam. You may use your set of molecular models

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1 CEM 203 Final Exam December 16, 2014 Your name: This a closed-notes, closed-book exam You may use your set of molecular models This test consists of 10 pages Time: 2h 30 min 1. / / / / / / / / 40 TTAL / 250 = / 100 This exam counts for 37.5% 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): -C 2 -C 3 Br S CF 3 N 2 C 3 C 3 C 2 C C 3 2 C C 2. (20 pts.) Write an accurate mechanism for the following known reactions: a. 1. MCPBA 2. NaN 3, then mild TsCl, pyridine 4. Zn, + (no mech. for this step), then aq. Na N b. excess C 3 S radical initiator SC 3 SC 3

3 Chem 203 final exam p. 3 of (30 pts) In the appropriate boxes, draw: a. The structure of a carbocation that is stabilized by N hyperconjugative interactions with C bonds, and that will rearrange to form a new carbocation stabilized by eight hyperconjugative interactions with C bonds: parent carbocation rearranged carbocation b. The structures of two isomeric alkenes that furnish only compound A upon treatment with 3 followed by Zn / + (write your answers in the appropriate boxes): A c. The structure of an alkyl halide that is likely to react with C 3 Na to give a product of substitution, and of one that is likely to react with C 3 Na to give a product of elimination: undergoes substitution undergoes elimination

4 Chem 203 final exam p. 4 of 10 d. Accurate mechanisms for an example of E2 reaction and an example of E1 reaction: E2 E1 e. The structure of an achiral molecule that is a meso form, and that of an achiral molecule that is not a meso form: achiral and meso achiral, but not meso f. Fischer projections of a D-aldonic acid and of the corresponding D-alditol: D-aldonic acid corresponding D-alditol

5 Chem 203 final exam p. 5 of (30 pts.) Indicate: a. the structure of the products obtained from the following reaction: C N and b. whether sugars i.-iv. below belong to the D or the L series (check the appropriate box): i. ii. iii. iv. L D L D L D L D c. the structure of the α-methyl furanoside obtained upon reaction of the D-pentose shown in part b. with C 3 and acid, and that of the β-methyl pyranoside obtained upon reaction of the L-hexose shown in part b. also with C 3 and acid: D-α-methyl furanoside L-β-methylpyranoside d. whether sugars i.-iv. above will react with NaB 4 to give one or two products (check the appropriate box): i. ii. iii. iv

6 Chem 203 final exam p. 6 of (30 pts) Complete the following equations by indicating all the reagents, in the correct order, that are required to achieve the stereoselective reactions shown. List the various reagents above / below the reaction arrows. Note: it is understood that chiral products obtained from achiral substrates will be racemic a. b. c. d. Br Br Br Br e. N 2 N 2

7 Chem 203 final exam p. 7 of (40 pts.) Draw the structure of the major product expected from the following reactions (write your answer in the boxes). If no change is predicted, answer "N REACTIN." a. 1. K Cl 2. Br 2, 2 3. Na b. 1. B , aq. Na 3. 2 Cr 4, aq. 2 S 4 c. 1. 2, 2 S 4 2. PCC 3. C 3 MgBr, then mild 3 + d. 1. Br 2. Mg 3. 2 C= 4. 2 S 4, heat 5. MCPBA 1. Cl 2, hv e. 2. K 3. 3, then Zn / + 4. NaB 4 5. Na, C 3 I

8 Chem 203 final exam p. 8 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. N 2 d. e. SC 3 C 3 f. Cl g. h. C 3

9 Chem 203 final exam p. 9 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 3

10 Chem 203 final exam p. 10 of 10 c. d. appy olidays!