You must have your answers written in PERMANENT ink if you want a regrade!!!! This means no test written in pencil or ERASABLE INK will be regraded.

Transcription

1 NAME (Print): SIGNATURE: Chemistry 310M/318M Dr. ent Iverson 3rd Midterm November 18, 2010 Please print the first three letters of your last name in the three boxes Please Note: This test may be a bit long, but there is a reason. I would like to give you a lot of little questions, so you can find ones you can answer and show me what you know, rather than just a few questions that may be testing the one thing you forgot. I recommend you look the exam over and answer the questions you are sure of first, then go back and try to figure out the rest. Also make sure to look at the point totals on the questions as a guide to help budget your time. You must have your answers written in PERMANENT ink if you want a regrade!!!! This means no test written in pencil or ERASABLE INK will be regraded. Please note: We routinely xerox a number of exams following initial grading to guard against receiving altered answers during the regrading process. FINALLY, DUE T SME UNFRTUNATE RECENT INCIDENCTS YU ARE NT ALLWED T INTERACT WIT YUR CELL PNE IN ANY WAY. IF YU TUC YUR CELL PNE DURING TE EXAM YU WILL GET A "0" N MATTER WAT YU ARE DING WIT TE PNE. PUT IT AWAY AND LEAVE IT TERE!!!

2 Page Points Total (29) (14) (16) (19) (6) (29) (28) (27) (17) (20) (21) (14) (11) (13) (10) (15) (289) % T Score W (W score + Exam Grade) Total Grade

3 onor Code The core values of the University of Texas at Austin are learning, discovery, freedom, leadership, individual opportunity, and responsibility. Each member of the University is expected to uphold these values through integrity, honesty, trust, fairness, and respect toward peers and community. (Your signature)

4 Compound pk a ydrochloric acid -Cl -7 Protonated alcohol RC ydronium ion Acetic acid Ammonium ion β-dicarbonyls 3 C 3 C- 4 N RC C 2 CR' Ethyl ammonium ion β-ketoesters β-diesters Water Alcohols Acid chlorides Aldehydes Ketones Esters 3 N C 2 C RC RC RC 2 RC 2 RC 2 RC 2 C 2 CR' C 2 CR' CCl C RC 2 CR' CR' Terminal alkynes RC C 25 LDA -N(i-C 3 7 ) 2 40 Terminal alkenes R 2 C C 44 Alkanes C 3 C 2-51

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6 Pg 1 (29) 1. (11 pts) What is the most important question in organic chemistry? Now in no more than two sentences, explain why the above is the most important question in organic chemistry. NTICE TIS!! 2. (10 pts) Amides are best represented as the hybrid of three contributing structures. Draw the second and third important contributing structures in the spaces provided, including all lone pairs and formal charges. For the two structures on the left in each problem, use arrows to indicate the movement of electrons to give the structures you drew. There is no need to draw any circles around any of these contributing strucures. You might want to read these directions again to make sure you know what we want C C N 3. (4 pts. each ) n the following structure, indicate the hybridization state of each atom indicated on the following radical 3 C C 3 2 N C 3

7 Pg 2 (14) 4. (14 pts) Consider the following statements. In the space provided write "a carbocation intermediate", "a radical intermediate" and/or "a single transition state with no intermediate" as appropriate. Answer(s) A. An S N 1 reaction involves B. An S N 2 reaction involves C. An E1 reaction involves D. An E2 reaction involves E. Stabilized by hyperconjugation F. Reaction of an alkane with 2, light involves G. Reaction of an alkene with, RR, light involves. Reaction of an alkene with NBS, light involves I. Reaction of an alkene with but no RR involves J. This is found in chain reaction mechanisms K. Intermediate most likely to rearrange L. Stabilized by resonance delocalization

8 Pg 3 (16) 5. (4 pts) For the following molecules, rank them from 1-4 according to overall alkene stability, with a 1 under the LEAST STABLE CATIN and a 4 under the MST STABLE CATIN. 6. (4 pts) For the following molecules, rank them from 1-4 according to overall alkene stability, with a 1 under the LEAST STABLE RADICAL and a 4 under the MST STABLE RADICAL. 7. (4 pts) For the following constitutional isomers, rank them from 1-4 according to overall alkene stability, with a 1 under the LEAST STABLE ALKENE and a 4 under the MST STABLE ALKENE. 8. (4 pts) For the following alkyl halides, rank them from 1-4 with respect to reactivity in an S N 1/E1 reaction, with a 1 under the LEAST REACTIVE ALKYL ALIDE, and a 4 under the MST REACTIVE ALKYL ALIDE.

9 Pg 4 (19) 9. (5 pts) A hydrogen bond is the strongest interaction seen among neutral molecules. In the space provided, draw two molecules of methanol (C 3 ) and show a hydrogen bond between them. Use a dashed line ( ) to indicate the hydrogen bond. Show all lone pairs. 10. (14 pts) Alcohols are good solvents for S N 1 and E1 reactions of secondary and tertiary alkyl halides in part because they interact strongly with the carbocation intermediate and halide anion formed in the first mechanistic step. These strong interactions lower the energy of the carbocation intermediate. For the following S N 1/E1 reaction, draw the carbocation intermediate and halide anion. Next draw a molecule of methanol interacting with the carbocation, and a different molecule of methanol hydrogen bonding to the halide anion. Use a dashed line ( ) to indicate a relatively strong interaction. Show all lone pairs and formal charges. 3 C C 3 C Cl C 3 3 C heat Draw the carbocation interacting with a methanol molecule here Draw the halide anion interacting with a methanol molecule here In the box provided draw the products of the above S N 1/E1 reaction. 3 C C 3 C Cl C 3 C 3 heat Product(s)

10 Signature Pg. 5 (6) 11. (8 pts.) Shown below are four different energy diagrams. Each is labeled with a letter. Use these letters to answer questions at the bottom of the page, and on the next TW mechansim pages. Potential Energy A Potential Energy B Reaction Coordinate Reaction Coordinate Potential Energy C Potential Energy D Reaction Coordinate Reaction Coordinate In the boxes provided, write the letter of the energy diagram that best describes the mechanism of the following reactions: C 3 C=C 2 + Cl 2 Cl Cl racemic Cl Cl Energy Diagram Letter C 3 C=C 2 + Cl C 3 CClC 3 Energy Diagram Letter + Cl Cl Energy Diagram Letter

11 Pg 6 (29) 12. (29 pts total) For each set of reagents below, draw the key transition state that occurs during the indicated reactions and then the product. Use dotted lines to indicate bonds that are in the process of being broken or made. Write all lone pairs of electrons any formal charges that you think are important. n the starting structures, draw all appropriate arrows to indicate the flow of electrons. Make sure to draw all the products that are produced including stereochemistry where appropriate. A. 3 C 2 C 3 C 3 C + C C I C 3 Transition State f the energy diagrams on the previous page, which one looks the most appropriate to describe this reaction (write the letter in the box that corresponds to the correct energy diagram) Products B. S + 3 C C C C 3 Transition State f the energy diagrams on the previous page, which one looks the most appropriate to describe this reaction (write the letter in the box that corresponds to the correct energy diagram) Products

12 Pg 7 (28) 13. (28 pts total) Complete the following mechanism for the reduction of an alkyne using sodium and ammonia. Use appropriate arrows to show movement of electron density, and show all non-bonding electrons as dots and show any formal charges. If any of the species are really a racemic mixtures of enantiomers, you only need to draw one stereoisomer and write "racemic" 3 C C C C C 3 + Na 3 C N Na N f the energy diagrams on the previous page, which one looks the most appropriate to describe this reaction (write the letter in the box that corresponds to the correct energy diagram) Products NTICE TIS QUESTIN AND TE TW SIMILAR QUESTINS N TE PREVIUS PAGE!!

13 Pg 8 (27) 14. (5 or 7 pts each) The following reactions all involve chemistry of alkyl halides. Fill in the box above the arrow with the mechanism that will be followed (S N 2, E2, etc.). Then draw only the predominant product or products and please remember that you must draw the correct stereoisomers. For S N 1/E1 reactions you must draw all significant products (including all stereoisomers). A. + Na N 3 B. 3 C 3 C 3 C + 3 C C C Na C. 3 C 3 C 3 C + 3 C S Na D. 3 C 3 C 3 C + C 3 C 2 E. 3 C I + C 3 C 2

14 Pg 9 (17) 14 (cont.) (5 or 7 pts each) The following reactions all involve chemistry of alkyl halides. Fill in the box above the arrow with the mechanism that will be followed (S N 2, E2, etc.). Then draw only the predominant product or products and please remember that you must draw the correct stereoisomers. For S N 1/E1 reactions you must draw all significant products (including all stereoisomers). These are a little harder so we gave you more room. ASSUME TAT N CARBCATIN INTERMEDIATES REARRANGE!! F. + 2 C 3 G. + C 3 C 2 Na. 3 C C 2 C 3 + C 3 C 2 Na

15 Pg 10 (20) 15. (3 or 5 pts each) For the following, complete the reactions with the predominant product or products. You must indicate stereochemistry with wedges and dashes. You must draw all stereoisomers produced as predominant products and write "racemic" under the structures when appropriate. Assume no rearrangments take place. 2 hν RR / hν 1) (sia) 2 B 2) 2 2 / C 3 2 Lindlar's catalyst C 3 2 Na, 2 N3 2 S 4

16 Pg 11 (21) 15. (3, 5 or 7 pts each) For the following, complete the reactions with the predominant product or products. You must indicate stereochemistry with wedges and dashes. You must draw all stereoisomers produced as predominant products and write "racemic" under the structures when appropriate. Assume no rearrangments take place. NBS hν 1) NaN 2 2) C 3 I C 3 P 3 C 3 C 3 NBS hν C 3 RR/ hν

17 Pg 12 (14) 16. (7 pts each) For the following sequences of reactions, work through all the different steps and then write the final product(s). Assume only the predominant product is formed at each step. You must indicate stereochemistry with wedges and dashes. You must draw all stereoisomers produced as predominant products and write "racemic" under the structures when appropriate. Assume no rearrangments take place. 1), RR, hν 2) Na 3) 2, 2 S 4, gs 4 1) Tos-Cl* 2) C 3 S Na 3) 2, Lindlar's catalyst *Tos-Cl = 3 C S 2 Cl C 3

18 Pg 13 (11) 17. These are synthesis questions. You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned provided that the product(s) you draw for each step is/are the predominant one(s). Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction. You must draw all stereoisomers formed, and use wedges and dashes to indicate chirality at each chiral center. Write racemic when appropriate. A) (4 pts)? B) (7 pts)?

19 Pg 14 (13) 17. These are synthesis questions. You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned provided that the product(s) you draw for each step is/are the predominant one(s). Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction. You must draw all stereoisomers formed, and use wedges and dashes to indicate chirality at each chiral center. Write racemic when appropriate. C) (13 pts)?

20 Pg 15 (10) 17. These are synthesis questions. You need to show how the starting material can be converted into the product(s) shown. You may use any reactions we have learned provided that the product(s) you draw for each step is/are the predominant one(s). Show all the reagents you need. Show each molecule synthesized along the way and be sure to pay attention to the regiochemistry and stereochemistry preferences for each reaction. You must draw all stereoisomers formed, and use wedges and dashes to indicate chirality at each chiral center. Write racemic when appropriate. All of the carbon atoms of the product must come from the starting material shown!! D) (10 pts)?

21 Pg 16 (15) 18. (15 pts) ere is an apply what you know question. Dr. Joe Bag'Doughnuts, a research chemist at the I.B. Dufus company, carried out the following reaction, and expected the four products shown. ( 3 C) 3 C C 3 I C 3 C 2 heat ( 3 C) 3 C ( 3 C) 3 C C 3 C 2 C 3 C 3 C 2 C 3 ( 3 C) 3 C ( 3 C) 3 C C 3 C 3 Dr. Bag'Doughnuts was surprised to find that he actually had eight products, that is four in addition to the above four. Based on your understanding of the reaction mechanism, predict what these other four products are. In no more than two sentences, explain how you came up with your answer. You can draw structures to help make your point, but you do not need to.