CHE 31: Organic Chemistry
Test 3
May 18, 1998

1. Multiple choice (2 points each)
Which of the following structures best represents the major form of glycine near its isoelectric point?

Which reason best explains why optically active amino acids are usually isolated from natural sources rather instead of synthesized using standard methods of organic chemistry?

What does the L in L-alanine signify?

Which of the following best describes the Edman degradation?

2. Provide the major products for the following reactions, showing stereochemistry where appropriate. (4 points each)

3. Cyclopropane derivatives can be prepared by a two-step base-catalyzed reaction of an a-chloroester with an a,b-unsaturated ester. The first step is a Michael addition and the second step involves an intramolecular reaction. Propose a mechanism to account for this transformation. Show all intermediate structures and use arrows to show the flow of electrons. (16 points)

4. Describe one of the reactions involved in either your pet molecule or your synthesis project. You should describe this reaction in detail, giving a mechanism for it. It is acceptable to use R for parts of the structure that are not directly involved in the reaction. (10 points)

5. Propose syntheses to accomplish the transformations shown. (10 points each)

Prepare BOC-Leu-Ala-Phe-OBn from its individual amino acids (or their protected forms). (If you prefer to use structural forms rather than three letter abbreviations, please see me for structures.)

6. Define the following terms and give examples with structures. (4 points each)