Dr. Steven Pedersen April 11, Chemistry 3B. Midterm 2. Student name: Answer Key Student signature: Lab section number (if you are in 3BL):

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1 Dr. Steven Pedersen April 11, 2011 Chemistry 3B Midterm 2 Student name: Answer Key Student signature: Lab section number (if you are in 3BL): Problem 1 (21 pts) Problem 2(a-c) (21 pts) Problem 2(d-g) (18 pts) Problem 3 (a-b) (16 pts) Problem 3 (c-d) (16 pts) Problem 4 (a-b) (20 pts) Problem 4 (c) Problem 5 Total Points (18 pts) (20 pts) (150 pts) o Calculators Allowed o Molecular Models Allowed Be Sure Your Exam has 9 Pages 1 3 Li 11 a 19 K 4 Be 12 Mg 20 Ca 5 B 13 Al 6 C 14 Si 7 15 P 8 16 S 9 F Br 53 I 2 e 10 e 18 Ar 36 Kr 54 Xe 1

2 1. (21 pts) Draw a structure for each of the following names. Follow any instructions that are provided next to the name. The hemiacetal derived from benzaldehyde and methanol (you do not need to show stereoisomers). C 3 The enol of acetaldehyde. The cyanohydrin derived from acetophenone and hydrogen cyanide (you do not need to show stereoisomers). C The ketal derived from acetone and 1,2-ethandiol. The hydrazone derived from formaldehyde and hydrazine, The aworth projection of a ketohexose in its α-furanose form (no credit will be given for a compound with two keto groups in it). ne possible answer D-1,4,5-trihydroxy-2-pentanone drawn as a Fischer projection with the carbonyl closer to the top of the projection. 2

3 2. Predict the product(s) of the following reactions. Where relevant, show all stereoisomers. Each redundant or wrong answer cancels one correct answer within any given box. (39 pts) 1. C 3 Li 2. 3 C 3 2 catalytic C 3 Two anomers can represented by a line drawn at the appropriate atom. + C 3 C 3, heat + 2 (more problems on the next page) major product only 3

4 + C catalytic C C C do not show cyanohydrins 2 Ph 3 P 1. Br Br Ph 3 P PPh Li 2 catalytic the major product 1. Li

5 3. Write logical arrow-pushing mechanisms for the following reactions. Be sure that your mechanism accounts for all products shown. (32 pts) C 3 catalytic + C 3 C 3 C 3 C 3 C 3 Alternative Mechanism C 3 C 3 C 3 catalytic More problems on the next page. 5

6 + C 3 catalytic C 3 C 3 C 3 2, heat 2 2 small amount of this formed Alternative mechanism from above intermediate 6

7 4. Rotundone is the compound that is thought to give black pepper its characteristic aroma. (J. Agri. and Food Chem., 2008, 56, 3788). A. A retrosynthetic analysis of Rotundone is shown below. Draw the structure of the compound that could lead to Rotundone under these conditions. (38 pts) C 3 C 3 (-) Rotundone B. Predict the product(s) of the following reactions involving Rotundone. The instructions for Question 2 on page 3 apply to this question as well. + Ph 3 P C 3 Ph 3 P three organic products + catalytic + 2 More Rotundone questions on the next page an enamine where all of the original stereocenters are preserved 7

8 C. Write logical arrow-pushing mechanisms for the following reactions. C 3 C 2 (small amount formed) C 3 C 2 C 3 C 2 C 3 C 2 (small amount formed) 8

9 5. Amomum aculeatum is an herb that is used in Indonesian folk medicine for curbing fever and treating malaria. A 2008 article in the Journal of atural Products (vol. 71, p. 390) examined the methanol extracts of the leaves of this plant. From these extracts several new compounds were isolated. The following questions deal with some of these compounds. (20 pts) A. If one were attempting to design a synthesis of Aculeatin A, a reasonable target would be one of the ketones shown in the box. Circle the best choice. (C 2 ) 12 C 3 (C 2 ) 12 C 3 (C 2 ) 12 C 3 (C 2 ) 12 C 3 (C 2 ) 12 C 3 Aculeatin A (C 2 ) 12 C 3 (C 2 ) 12 C 3 B. The ketals shown below were also isolated from the extracts mentioned in the introduction to this problem. What stereochemical term best describes the relationship between these two compounds?answer goes here: DIASTEREMERS C 3 C 3 3 C( 2 C) 14 ketal X 3 C( 2 C) 14 ketal Y C. The authors of the J. atural Products paper suggest that the ketals X and Y (Part B) are produced by Amomum aculeatum. Considering that these compounds were isolated from methanol extracts under neutral or slightly acidic conditions, draw the structure of E compound that could have given rise to BT ketals X and Y under the extraction conditions. int: the compound is not a ketone. EVERYE RECEIVED 6 PITS FR TIS QUESTI 9