Note: You must have your answers written in pen if you want a regrade!!!!

Transcription

1 NAME (Print): SIGNATURE: hemistry 310M/318M Dr. Brent Iverson 2nd Midterm November 1, 2007 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. Note: You must have your answers written in pen if you want a regrade!!!!

2 Page Points Total (20) (25) (24) (20) (21) (-) (28) (14) (14) (10) (15) (21) (9) (24) (245) W T Score

3 onor ode 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 ompound pk a ydrochloric acid -l -7 Protonated alcohol R ydronium ion Acetic acid Ammonium ion!-dicarbonyls N R 2 R' Ethyl ammonium ion!-ketoesters!-diesters Water Alcohols Acid chlorides Aldehydes Ketones Esters 3 N R R R 2 R 2 R 2 R 2 2 R' 2 R' l R 2 R' R' Terminal alkynes R 25 LDA -N(i- 3 7 ) 2 40 Terminal alkenes R 2 44 Alkanes

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6 Pg 1 (20) 1. (5 pts) What is the most important question in organic chemistry? 2. (10 pts) Write an acceptable IUPA name for the following two molecules. Where appropriate, use E and Z or R and S. 4. (5 pts) Draw a structure that corresponds to the following name: (3E,5Z,7Z)-1,3,5,7,10-undecapentaene

7 Pg 2 (25) 5. (2 pt each) A) For each atom indicated, state the hybridization state in the box provided. N 3 N S N Ampicillin B) (1 pt. each) n the above structure, put an asterisk next to each chiral center. ) (3 pt. each) The ampicillin structure shown is the single enantiomer used to treat bacterial infections. Given the number of chiral centers you identified, how many total stereoisomers are theoretically possible for the above molecule? D) (3 pt) Is the ionic form of ampicillin shown above the form that predominates at p 2.0, 7.0, or 13.0? (int: use the pka table provided for guidance) E) (3 pt) At p of 2.0, what is the total charge on the ampicillin molecule? (int: use the pka table provided for guidance)

8 Pg 3 (24) 6. (6 or 10 pts each) Label each stereocenter as "R" or "S" and on the line provided state whether the pair of molecules represent two enantiomers, two diastereomers, or the same compound. Draw a circle around any meso compound. A. Br Br B. 7. (2 pts. each )n the following structure, describe the bonds indicated in terms of overlap between hybrid orbitals (the valence bond approach). For example, an answer might be! sp 3 -sp 3 Note: ignore hyperconjugation effects for this question. N

9 Pg 4 (20) 8. (20 pts. total) Rank the following species in terms of the stated property from 1 to 4 (or 3) as described, with intermediate numbers to rank the species of intermediate stability activity. Please make sure you know what we want, as you will get no credit if you get the numbers backwards! Stability of carbocations: Place a 1 under the most stable carbocation and a 5 under the least stable carbocation Relative Acidity: Place a 1 under the most acidic molecule and a 4 under the least acidic molecule. N Relative Acidity: Place a 1 under the most acidic molecule and a 3 under the least acidic molecule. F F F F F F F F F Relative Acidity: Place a 1 under the most acidic molecule and a 4 under the least acidic molecule. F Br l I Relative Acidity: Place a 1 under the most acidic molecule and a 4 under the least acidic molecule. l

10 Pg 5 (21) 9. (3 pts each) Use your understanding of relative acidities to predict the position of equilibrium in the following acid-base reactions. Draw a circle around the side of each equation that predominates at equilibrium. These may seem difficult at first, but remember what you know about acid-base equilibria as well as relative acid strenghts. 3 2 S Na 3 2 S Na Na 3 Na Li Li 10. (12 pts) For the following carbocation, write the hybridization state for each atom indicated by the arrows. Next, circle all of the sigma bonds that operate to stabilize this carbocation through hyperconjugation.

11 Signature Pg. 7 (28) 12. (20 pts.) Read these directions carefully. Read these directions carefully. (It was worth repeating) For the reaction of propene with with l 2 in the presence of EXESS 2 shown below, fill in the details of the mechanism. Draw the appropriate chemical structures and use an arrow to show how pairs of electrons are moved to make and break bonds during the reaction. MAKE SURE T FILL IN TE BLANKS AT TE BTTM. For this question, you must draw all molecules produced in each step (yes, these equations need to be balanced!) l l.. Intermediate A Products Intermediate B (4 pts) During the reaction described by the above mechanism, say what happens to the p of the solution (4 pts) Is this reaction catalytic in acid? NTIE TESE TW

12 Signature Pg. 8 (14) 11. (cont.) (4 pts.) A. For the reaction mechanism you drew on the previous page, circle the energy diagram that best describes your mechanism. Sorry about the lame curves, imagine they are smoother! Potential Energy Potential Energy Reaction oordinate Reaction oordinate Potential Energy Potential Energy Reaction oordinate Reaction oordinate B. (4 pts.) Now draw an X through the energy diagram that best describes the reaction of an alkene with l 2 (with no water in the reaction).. (3 pts each) For the following, circle the capitalized word that best completes the statement. For a reaction that has a favorable motive (thermodynamic driving force) as written, the products are LWER or IGER in energy than the starting materials. A reaction that has greater opportunity (occurs faster) has a LWER or IGER activation energy.

13 Pg 9 (14) 12. (14 pts) The following molecule undergoes a rearrangment. Draw the first carbocation intermediate in the first box, then the rearranged carbocation intermediate in the second, and finally the rearranged product of this reaction. For each step, include all products, all lone pairs and formal charges. Use arrows to indicatethe flow of electrons involved in each step. A. + Br First carbocation intermediate Rearrangement Br Product Rearranged carbocation intermediate

14 Pg 10 (10) 11. (5 pts each) The following reactions all involve chemistry of alkenes. Fill in the box with the product(s) that are missing from the chemical reaction equations. Draw only the predominant regioisomer product or products (i.e. Markovnikov or non-markovnikov products) and please remember that you must draw the structures of all the product stereoisomers using wedges and dashes to indicate stereochemistry. When a racemic mixture is formed, you must write "racemic" under both structures EVEN TUG YU DREW BT STRUTURES. A. Br B g(ac) NaB 4

15 Pg 11 (15) 12. (cont.) (5 pts each) The following reactions all involve chemistry of alkenes. Fill in the box with the product(s) that are missing from the chemical reaction equations. Draw only the predominant regioisomer product or products (i.e. Markovnikov or non-markovnikov products) and please remember that you must draw the structures of all the product stereoisomers using wedges and dashes to indicate stereochemistry. When a racemic mixture is formed, you must write "racemic" under both structures EVEN TUG YU DREW BT STRUTURES. D. 1) B 3 2) 2 2 / E. Br 2 / 2 F. l 2

16 Pg 12 (21) 12. (cont.) (5 pts each) The following reactions all involve chemistry of alkenes. Fill in the box with the product(s) that are missing from the chemical reaction equations. Draw only the predominant regioisomer product or products (i.e. Markovnikov or non-markovnikov products) and please remember that you must draw the structures of all the product stereoisomers using wedges and dashes to indicate stereochemistry. When a racemic mixture is formed, you must write "racemic" under both structures EVEN TUG YU DREW BT STRUTURES. G. 2 2 S 4 (catalytic) 13. (4 or 6 pts each) The following problems are a new format. We turn the tables and give you the product. In the space provided show the starting material required to make that product using the given reagents. When more than one starting material would work, you must draw both. A. 2 2 S 4 (catalytic) 3 B. Br Br Br Br (Racemic Mixture) 3 Br. 1) B 3 2) 2 2 / (Racemic Mixture)

17 Pg 13 (9) 13. (9 pts total) When making an alcohol from an alkene it may be important (for physical properties of a desired material or for biological activity of a desired drug) to insert the group at a specific carbon with a specific stereochemistry. For instance 3-methyl-1-butene, shown below, can be converted into several types of alcohols depending on what hydration reagent(s) a chemist uses. In the three boxes below write the reagent(s) that will produce the products shown. G Racemic 3 3 These are the three possible products methyl-1-butene 3 This is the only product Racemic These are the only products 3 3

18 Pg 14 (24) 14. For the following reaction, draw all of the expected products including the different regioisomers and stereoisomers. As an aid in understanding the stereochemistry of the starting material, we have drawn the chair form just below. Like before, write racemic if a racemic mixture is produced. IT is K to draw the products in whatever format you are most comfortable with (flat rings with wedges and dashes, etc.); the chair version was only included to help you understand the starting material. A) (12 pts) Assume no rearrangment. l hair form of starting material B) (6 pts) For the above mixture of products you drew for part A), would your product mixture rotate the plane of plane polarized light? Explain your answer in one or two sentences. ) (6 pts) For the above products from part A), circle the two that will form the most stable chair conformations.