CHEM 203. Midterm Exam 2 November 12, 2013 ANSWERS. This a closed-notes, closed-book exam. You may use your set of molecular models

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1 CEM 203 Midterm Exam 2 November 12, 2013 ANSWERS Your name: This a closed-notes, closed-book exam You may use your set of molecular models This document contains 7 pages Time: 1h 30 min 1. / / / / / / 20 TOTAL / 100 This exam counts for 18.75% of your CEM 203 final grade

2 Chem 203 midterm exam 2 p. 2 of 7 1. (10 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 3 OSO 2 CF 3 O-C 2 C 3 C=C 2 -O C 3 O -N (15 pts.) The radical chlorination of compound A afforded a mixture of products, from which five distinct mono-chlorinated derivatives were isolated. Draw the structures of the five monochloro products in the boxes below. monochloro product 1 monochloro product 2 A 2 hν monochloro product 3 monochloro product 4 monochloro product 5 3. (15 pts.) Inside the appropriate boxes, draw: a. The structure of an alkyl bromide that furnishes alkene A when treated with potassium tert-butoxide, but alkene B as one of the products obtained upon heating in C 3 O: OK C 3 O heat B A (one of the products)

3 Chem 203 midterm exam 2 p. 3 of 7 b. The structure of an alkyne that yields one product when treated with 2 in the presence of catalyst, and then with OsO 4 followed by aqueous NaSO 3 solution, but a different product when treated with Na in liquid N 3, and then with OsO 4 followed by aqueous NaSO 3 solution. structure of the alkyne in question c. The structure of an alkene that yields a chiral product when treated with 2, but an achiral product when treated with OsO 4 followed by aqueous NaSO 3 solution: structure of the alkene in question d. The structure of an alkene that yields only product C when treated with O 3 and then with Zn / +, followed by C 3 C 2 Mg and then mild 3 O + : 1. O 3 2. Zn, + (or cis isomer) 3. C 3 -C 2 Mg 3. mild 3 O + O C e. The structure of an alkyl halide that cannot undergo E2 reaction other answers are possible

4 Chem 203 midterm exam 2 p. 4 of 7 4. (20 pts.) Provide the structure of the major product expected from the following reaction sequences. If no overall change is expected, answer "NO REACTION." Important: compounds incorporating multiple stereogenic centers must be drawn with the correct relative configuration. Note: it is understood that chiral compounds will be obtained as racemic mixtures. a. 2 hν b. C 3 1., radical 2. C 3 Li Cu no reaction 1. NBS, radical c. 2. Na 3. 2, catalyst C 3 d AIBN, heat OK Ph Ph Ph polystyrene n Ph = phenyl e. 1., radical 2. NaN 3 3. Zn, + N 2

5 Chem 203 midterm exam 2 p. 5 of 7 5. (20 pts.) Propose a method to achieve the transformations shown below. Indicate all the reagents, in the correct order, that are required to induce each transformation. Present your answer as a numbered list displayed above / below each reaction arrow. If a product appears to be unavailable from the indicated starting material by any method known to you, write "INACCESSIBLE" on the reaction arrow Note: it is understood that chiral compounds will be obtained as racemic mixtures. a SO 4, heat O 2. N 2 3. NaN 3 4. Zn, , hv b. S 2. Na 2 S c. O NaN 3 3. Zn, + O N 2 d SO 4, 2 O 2. 2 SO 4, heat 3. 2, 2 O 4. NaSC 3 O SC 3 1. NBS, rad. init. 2. tert-buok e. O 3. O 3, then Zn/ + 4. C 3 Mg, then mild 3 O + other answers are possible

6 Chem 203 midterm exam 2 p. 6 of 7 6. (20 pts.) Propose a method for the preparation of compounds a. e. below starting ONLY with methane (C 4 ) and acetylene ( C C ) as the source of carbon atoms. You may use any additional reagent that might be needed (e.g., borane,, Mg, 2 O 2, potassium tertbutoxide, etc.). Present your answer as a clear flowchart that shows all intermediate steps and products. Substances obtained in a prior sequence may be used in later sequences. It is not necessary to draw mechanisms a. C 4 2, hv C 3 2, cat. C 3 C 3 NaN 2 C 3 C 3 NaN 2 C 3 b. COO cat., 2 1. O O 2, + NaN 2 cat., 2 (twice) c. O C 3 (from a.) cat., 2 1. B O 2, aq. NaO cat., 2 NaN 2 Na/N 3 (liq) instead of 2 / would be OK in the above cases

7 Chem 203 midterm exam 2 p. 7 of 7 d. N 2 1. NaN 3 2. Zn, + product a. NaN 2, rad. cat., 2 e. O O 1. OsO 4 2. aq. NaSO 3 Na liq. N 3 NaN 2 C 3 (from a.) from c. alternative answers may be OK