Problem_Set_8 - thioester to be more or less readily...

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Chem 358 Spring 2007 Problem Set #8 Text Problems Chapter 21: 21.31-34, 37-39, 41, 45, 47, 50, 52, 55, 56, 57, 59 Additional Problems 1. (Prelim 2, 1999) Amides are planar and exist as the cis and trans isomers shown below on the left. Thioesters are also planar and the cis and trans isomers are shown on the right. R N R O H R N H O R R S R O R S O R trans (E) cis (Z) trans (E) cis (Z) amide thioester Would you predict that the barrier to cis-trans conversion is bigger in an amide or in a thioester? (b) Write a detailed mechanism for the base-catalyzed hydrolysis of a thioester. Clearly label the addition and elimination steps and identify the tetrahedral intermediate. Use curved arrows to show the flow of electron pairs. The reaction is shown below. R S R' O HO H 2 O R OH O HSR' (c) Based on your answer to part (a) and your knowledge of the base - catalyzed hydrolysis of amides would you expect the
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Unformatted text preview: thioester to be more or less readily hydrolyzed by base? 2. How would you synthesize the molecule shown below from the starting material provided? The desired product is a potent antihistamine used in several decongestants. Cl N N Cl N CO 2 H from 3. (Prelim 2, 1999) Propose a practical laboratory synthesis for the molecule shown from bromocyclohexane. Use any other organic reagent with no more than one functional group and four or fewer carbons as the starting material and appropriate inorganic reagents. OH from Br 4. Supply the missing reagents and reaction conditions (a) (g) for each transformation, some of which require more than one step. In some cases you may have to refer to earlier chapters. OH CO 2 CH 3 O O OH OH O OH O COOH O CO 2 CH 3 CO 2 H O O O O (a) (b) (c) (d) (f) MnO 2 (e)...
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