Organic Chem Chirality/R&S/Substitution/Elimination

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Name__________________________

Chemistry 190: Organic Chemistry

EXAM 3
Thursday April 21, 2011

1. (12) ______ 2. (14) ______ 3. (20) ______ 4. (12) ______ 5. (54) ______ 6. (16) ______ 7. (12) ______ 8. (10) ______ Total (150) ______

The exam consists of twelve numbered pages and an unnumbered cover sheet. Make certain that you have a complete exam. You will have two hours to work on the exam. No books or notes are allowed; however, you may use a molecular model set and a calculator. For full credit, please show all of your work. Read all of the questions carefully. You are advised not to spend an inordinate amount of time on any one question until you have attempted all of the others. If you get stuck on a problem, write down what you can on it and then try to finish it when you have worked through everything else.

Good Luck!

1. (12 points) Butaclamol is an antipsychotic drug that is prescribed for the treatment of schizophrenia. The structure of butaclamol is shown below. Determine the configuration (R or S) for each of the chiral centers in this compound. For full credit (or partial credit if your configuration is incorrect), please show (clearly labeled) how you have prioritized the groups. Also, be certain to clearly indicate which set of priorities/configuration goes with which chiral center. OH N H H C(CH3)3

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2. (14 points, 7 points each) For each of the following pairs of reactions, indicate what type of reaction would be occurring (SN1, E1, SN2, E2). Then, circle the reaction that would have the larger rate constant (i.e. the faster reaction under identical conditions of concentration and temperature). If the rate constants for the two reactions would be equal, write “EQUAL”. Briefly explain your answers. O O S CH3

a)

+

NaOH

OH +

O O S CH3

O O S CH3 + O NaOH OH +

O O S CH3 O

Reaction type: _________

2

b) + (CH3)3COI + (CH3)3COH + I-

+ (CH3)3COI

+ (CH3)3COH + I-

Reaction type: _________

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3. (20 points total, 5 points each) For each of the following reactions, either predict the major product or indicate the necessary reagent(s). Pay attention to stereochemistry, where necessary. In each case there is only one major product.

a) 1) Hg(OAc)2, H2O 2) NaBH4, NaOH

b)

I

NaSH

c)

HBr, ROOR, Δ

d) OH

H2SO4 Δ

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4. (12 points total) One method for synthesizing amino acids involves reducing an imine derivative as shown in the reaction below for the formation of the amino acid serine. OH COOH N H H2 catalyst OH COOH NH2

a) (3 points) The amino acid product above is shown without specifying the stereochemistry. Draw a structure that shows a clear representation of the (S)-enantiomer of serine.

b) (3 points) This reduction reaction can be carried out with an achiral catalyst such as palladium metal. The molecular weight of serine is 105 g/mol. The specific rotation of optically pure (S)serine is +14.0°. What would the observed rotation be for a sample of serine prepared by this method using a palladium catalyst. Assume that the concentration of the sample is 1.0 M and that the rotation was measured in a 10 cm sample cell.

c) (6 points) The reaction can also be done using a chiral catalyst. When a 1.0 M sample of serine produced by reaction with a chiral catalyst is examined in a 10 cm sample cell, the observed rotation is found to be 1.1°. What percentage of this sample consists of the (S)enantiomer?

5

5. (54 points total) Predict the major product(s) of the following reactions. Indicate stereochemistry where necessary and clearly indicate how you have determined the stereochemistry. In each case, indicate which reaction(s) is(are) occurring (i.e. SN1, SN2, E1, E2). Also, in each case write a complete mechanism that explains the formation of each product. Note: In reactions that are SN2 or E2 there should be just one major product. In reactions that are SN1 and/or E1 you should indicate all products that would...
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