Download CHEM 238 Exam 1 - Organic Chemistry Reactions and Mechanisms and more Exams Organic Chemistry in PDF only on Docsity! CHEM 238 Summer, 1999 EXAM #1 Name . Prof. Sasaki 100 points TOTAL Good Luck! Note: Only answers in the box will be graded. ________________________________________________________________________ 1. (25) In order to test relative rates of intermolecular and intramolecular proton transfer reactions leading to E2 eliminations, the following two experiments were carried out with the results shown. The intermolecular reaction: O- K+ H + CH2Br H 20 days no elimination reaction The intramolecular reaction: O- K+ H H CH2Br < 1 hr OH H CH2 , O- K+ H CH2Br H compound A (a) Draw a mechanism using the curved-arrow conversion showing how the intramolecular E2 reaction occurs. (b) A stereoisomer of the compound shown above (compound A) has the bromomethyl group (-CH2Br) on the same side of the ring as the hydroxyl group. This compound does not undergo an elimination reaction, but gives a different product. Predict what this product is by writing a mechanism using curved arrows. CHEM 238 page 2 Name . 2. (25) (a)When the tosylate of 3-methyl-3-phenyl-2-butanol is heated, 2-methyl-3-phenyl- 2-butene is formed. In order to determine the mechanism of this reaction, the compound was prepared with a radioactive carbon-14 (14C) label at the tosylate carbon. The results of the experiment with the labeled compound are shown below. H3C C CH3 14C OTs CH3 H 3-methyl-3-phenyl- 2-butyl tosylate heat H3C C H3C 14C CH3 2-methyl-3-phenyl- 2-butene Draw a stepwise mechanism for the reaction. Use curved arrows to indicate the movement of electrons. (Hint: Describe out the changes in connectivity that occur in the reaction) (b) The following reaction was used in the synthesis of (+)-asteriscanolide, a natural product. (Do not get intimidated by the size of compounds!) O O H CH3 H3C H3C O O H CH3 H3C H3C HO stereochemistry of OH and CH3 not shown A B (i) What reagents would you use for steps A and B? A B (ii) Two approaches to the double bond by the reagents are possible. Reaction at one face of the double bond rather than the other is highly favored. Draw a structural formula that clearly shows what you think the stereochemistry of the final product will be.
