CHEM 203. Midterm Exam 2 November 13, 2014 ANSWERS. This a closed-notes, closed-book exam. You may use your set of molecular models

Transcription

1 CEM 203 Midterm Exam 2 ovember 13, 2014 Your name: ASWERS 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 TTAL / 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.) The compounds shown below are similar though clearly not identical to particular reagents that were discussed in class. n the basis of analogy, indicate the likely use of each (write your answers in the appropriate boxes): radical initiator (cf. AIB; notes of ct 15) Cl controlled release of Cl 2 (cf. BS; notes of ct 22) Si a Si strong base (cf. a 2 ; notes of ct 20) radical inhibitor (cf. BT; notes of ct 15) C 3 2. (15 pts.) Inside the appropriate boxes, draw: a. The structure of an alkane that is a poor substrate for radical chlorination, but a good one for radical bromination, and one that is a poor substrate for radical bromination, but a good one for radical chlorination: poor for chlorination, good for bromination poor for bromination, good for chlorination C 3 C 3 b. The structure of an alkyl halide that is likely to react with C C a by the S 2 mechanism, and one that is likely to react with the same reagent by the E2 mechanism. likely to react by S 2 likely to react by E2 I

3 Chem 203 midterm exam 2 p. 3 of 7 c. The structure of two carbonyl compounds that yield product A when treated with an excess of C 3 Mg, followed by mild 3 + : or C 3 C 3 Mg then mild 3 + A d. The structure of a chiral alkyne that yields a chiral product when treated with 2 and catalyst, but an achiral product when treated with 2 and finely divided platinum: e. The product obtained from alkene B upon reaction with, followed by C 3 Li and Cu: 1. B 2. C 3 Li Cu 3. (15 pts.) Write an accurate mechanism for the following known reaction: R R 2 R C 3 S SC 3 C 3 S radical initiator C 3 S [ + C 3 S ] C 3 S = C 3S C 3 S SC 3

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 " REACTI." Important: compounds incorporating multiple stereogenic centers must be drawn with the correct relative configuration. ote: it is understood that chiral compounds will be obtained as racemic mixtures. a. 1. 2, C 3 2. a 3 3. Zn, + 2 C 3 (or enantiomer) b S 4, 180 C 2. I 3. a 4. a, liq. 3 C 3 c. 1., radical initiator 2. C 3 Mg Cu 1. Cl d. 2. C 3, heat C 3 and (2 products) e. C 3 1. BS, hν 2. Mg 3. C 2 4. mild 3 +

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 "IACCESSIBLE" on the reaction arrow ote: it is understood that chiral compounds will be obtained as racemic mixtures. 1. BS, hν a. 2. K 3. B , aq. a b. 1. a 2, then C 3 I 2. a, liq c. 1. 3, then Zn, + 2. C 3 Mg 3. 2 S 4, heat 1. Cl 2, hν d. 2. K 3. BS, hν 4. C 3 Mg, Cu e C 3 Sa SC 3

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 LY with methane (C 4 ) and acetylene ( C C ) as the source of carbon atoms. You may use any additional reagent that might be needed ( borane, Cl, Mg, 2 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. ** 2 2 S 4 2 * C 3 Cl a + a 2 a + C 3 Cl a 2 C 4 Cl 2, hν C 3 Cl * a / 3 (leading to the trans-isomer) K here ** B 3 then 2 2 and aq. a K for this step b. 3, then Zn / + 2 ** 2 * C 2 =C 2 a + a + a 2 ** a / 3 (leading to the trans-isomer) K here * a / 3 K in this step

7 Chem 203 midterm exam 2 p. 7 of 7 c. B 3, then 2 2, aq. a 2, (a / 3 K, too) a + d. C 3 a, then C 3 -Cl (part b.) Mg (part b.) 2 *, rad. initiator Mg (Li K, too) * a / 3 K in this step e. C 3 2 C 3 a + C 3 2, C 3 C 3 Cl a C 3 2, (a / 3 K, too) (alternative answers may be acceptable)