Chemistry 143 Exam #2 November 15, 2017 Name: Student Number: Section Number: TA: INSTRUCTINS: This exam consists of 32 questions on 9 pages. Please make certain that your exam is complete. Write your name, student number, and section number on both the exam and answer sheet. Be certain to bubble in your PID digits on the answer sheet. The absence of any of these identification items will result in deduction of 2 points from your score. Questions 1-28 are each worth 3 points. Question 28-32 are worth the points indicated. Write your answers to Questions 1-28 on the enclosed answer sheet. Write your answers to Questions 29-32 in the space provided on this exam. When you complete the exam, insert your answer sheet into your exam and hand both in on the bench in front of the lecture hall in the spot indicated by your section number. 1
1. Which of the following molecules has a stereogenic carbon atom C 3 2 CCC 3 1 C 3 CCC 3 C 3 CC 3 C 3 CCC 3 3 2C C 3 3 4 (a) 1 (b) 2 (c) 3 (d) 4 (e) 2, 3 (f) 1, 4 2. Which of the following groups has the highest priority for assigning R and S absolute configuration C N C C 2 N 2 C C C (a) (b) (c) (d) (e) (f) 3. The correct name for the structure given below is I (a) (2R, 4R)-2-chloro-4-iodopentane (b) (2S, 4S)-2-chloro-4-iodopentane (c) (2R, 4S)-2-chloro-4-iodopentane (d) (2S, 4R)-2-chloro-4-iodopentane 4. Identify the E-alkene(s) from the following possibilities: C 2 C3 C 2 C 3 C 2 C 2 C2 C 3 C 2 C 3 3 C C 2 C 3 C 2 C 3 1 2 3 4 (a) 1, 2 (b) 3, 4 (c) 1 (d) 2 (e) 3 (f) 4 5. Which of the following structures corresponds to 4-(R)-chloro-3-methyl-2-(Z)-pentene 3 C C 3 C 3 3 C C 3 C 3 (a) 1 (b) 2 (c) 3 (d) 4 6. Which of the following is TRUE 1. A 50:50 mix of enantiomers rotates plane-polarized light to the left (levorotatory). 2. A 50:50 mix of enantiomers rotates plane-polarized light to the right (dextrorotatory). 3. A 50:50 mix of enantiomers does not rotate plane-polarized light. 4. A 50:50 mix of enantiomers is a racemic mixture. 5. A 50:50 mix of enantiomers is a diastereomeric mixture. (a) 1, 4 (b) 1, 5 (c) 2, 4 (d) 2, 5 (e) 3, 4 (f) 3, 5 3 C C 3 C 3 3 C 1 2 3 4 C 3 C 3 2
Questions 7-10 refer to the following molecules: C 2 C 2 C 2 C 2 C 2 C 2 C 2 C 2 1 2 3 4 C 2 C 2 5 6 7 8 7. Identify the molecule that is the enantiomer of 6. (a) 1 (b) 2 (c) 3 (d) 4 (e) 5 (f) 7 (g) 8 8. Identify the diastereomer(s) of 8. C 2 C 2 C 2 C 2 (a) 2 (b) 4 (c) 5 (d) 7 (e) 2 and 5 (f) 4 and 7 9. Identify the molecules that will not rotate plane-polarized light. (a) 2, 3 (b) 5, 6 (c) 4, 7 (d) 2, 5 (e) 3, 6 (f) 1, 8 10. Which of the statements is true concerning 7. (a) 7 has the same melting point as 4. (b) 7 has three stereogenic centers. (c) 7 has four stereogenic centers. (d) 7 has two stereogenic centers with absolute configuration of S. (e) none of the above. 11. Which statements related to the mixture formed in the following reactions are TRUE: + 1. The two s formed are a mixture of enantiomers. 2. The two s formed are a mixture of diastereomers. 3. The two s are formed at the same rate and in the same amounts. 4. The two s are formed at different rates and in different amounts. 5. The mixture will rotate plane-polarized light. 6. The mixture will not rotate plane-polarized light. C 2 C 2 (a) 1,3,5 (b) 1,3,6 (c) 1,4,6 (d) 2,3,5 (e) 2,4,5 (f) 2,4,6 3
12. Which of the following FUR statements about S N 1 and S N 2 reactions are TRUE: 1. For S N 1 reactions, primary organic halides react faster than tertiary organic halides. 2. For S N 1 reactions, tertiary organic halides react faster than primary organic halides. 3. S N 1 reactions proceed with racemization. 4. S N 1 reactions proceed with inversion of configuration. 5. For S N 2 reactions, primary organic halides react faster than tertiary organic halides. 6. For S N 2 reactions, tertiary organic halides react faster than primary organic halides. 7. S N 2 reactions proceed with racemization. 8. S N 2 reactions proceed with inversion of configuration. (a) 2,3,6,7 (b) 1,4,5,7 (c) 2,4,5,8 (d) 1,4,6,7 (e) 1,3,6,8 (f) 2,3,5,8 13. What is the mechanism of the following reaction: C 3 C 2 +, heat 2 C C 2 + 2 (a) S N 1 (b) S N 2 (c) E1 (d) E2 (e) S N 1, S N 2 (f) S N 2, E2 14. Rank the anions below starting from most stable and ending at least stable: 3 C C 3 C C 3 C 3 C 2 1 2 3 (a) 1, 2, 3 (b) 1, 3, 2 (c) 2, 3, 1 (d) 2, 1, 3 (e) 3, 1, 2 (f) 3, 2, 1 15. Rank the acids below starting from most acidic and ending at least acidic: C 3 3 C C C 3 C 2 C 3 1 2 3 (a) 1, 2, 3 (b) 1, 3, 2 (c) 2, 3, 1 (d) 2, 1, 3 (e) 3, 1, 2 (f) 3, 2, 1 Questions 16-22 are to be answered from the following choices. An answer may be used more than one time. A K B C D E Jones reagent Na mcpba F G I K PCC J 4
16. Mg 1) 2) 2, + 17. 18. 19. K 20. C 3 C 2 Mg 1) 2) 2, + 3 C C 3 C 3 C 2 21. Na 22. + 2 N N C 3 3 C 3 C N N Questions 23-28 are to be answered from the following choices. An answer may be used more than one time. A B C D CN E F G I CN no reaction N 2 J 23. CN, K 24. Na 5
25. Mg, TF Mg 26. 2 27. N 2 N 28. Na 29A. (4 pts) In the reaction of (R)-3-iodo-3-methylhexane with sodium ethoxide, a reactive intermediate is formed before formation of NaI and two additional s. Insert NE ARRW on the structure of (R)-3-iodo-3-methylhexane to indicate mechanistically the formation of the reactive intermediate. Draw the reactive intermediate and the two s in the appropriately labelled boxes. (INT: S N 1 mechanism) I Na reactive intermediate + + NaI 29B. (1 pt) QUESTIN: The mixture of this reaction rotates plane-polarized light. TRUE FALSE 6
30. (3 pts) For the acid-catalyzed dehydration of 1-methylcyclohexanol, draw the structure of the initially formed conjugate acid and the two s formed after the dehydration in the boxes provided below. Be sure to include any charges. (int: E 1 elimination). + - 2 reactive intermediate conjugate acid - + + 7
31. (4 pts) Reaction of benzaldehyde with + and methanol results in formation of benzaldehyde hemiacetal. Using the structure of benzaldehyde and + already provided, draw NE ARRW that indicates formation of intermediate 1. Then draw the structures of intermediate 1 and 2 in the boxes provided. Be certain to show all charges. In the presence of excess + and methanol, benzaldehyde acetal is formed. Draw the structure of benzaldehyde acetal in the box provided. (int: benzaldehyde acetal has no charges.) + C 3 benzaldehyde intermediate 1 intermediate 2 - + +, C 3 C 3 benzaldehyde hemiacetal benzaldehyde acetal 8
32. (4 pts) For the reaction of methylmagnesium bromide with butanal: 1. Using the structures given, draw TW ARRWS that mechanistically describe the reaction between the two reagents. 2. Suggest a specific solvent that could be used for the reaction of methylmagnesium bromide with butanal. 3. Draw the structures of the intermediate formed in the reaction. Be sure to show where the Mg +2 and - reside in the intermediate. 4. Draw the structure of the formed after addition of + and 2 to the intermediate. Bys do not need to be shown. +2 C 3 Mg solvent intermediate +, 2 Nucleophile (only) S RS Nucleophile (only) 2 S RS Base (only) 1 S N 2 2 S N 2 + S N 1 3 S N 1 Strong Nuc/ Strong Base C 3 C 3 C 2 Strong Nuc/ Strong Base Weak Nuc/ Weak Base 2 C 3 C 3 C 2 1 E2 + S N 2 2 E2 + S N 2 3 minor major E2 major minor Base (only) 1 2 E2 E2 Weak Nuc/ Weak Base 1 2 S N 2 + E2 S N 2 + S N 1 + E1 + E2 3 E2 3 S N 1 + E1 9