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Quiz7cor_E - hemiacetal 2 Draw the TLC you’d expect to...

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1 CHM 2123, Quiz #7: Preparation of a Cyclic Ketal MARKING SCHEME Assigned: October 29, 2009 Due: November 2, 2009, before 5pm 1. Your lab manual specifies that your reaction flask (the Erlenmeyer) must be dry. How could water interfere with the progress of the reaction? Explain with a mechanism (hint: look at the mechanism in the introduction for this experiment… notice the reaction arrows!). (3 points) According to LeChatelier’s principle, water must be taken away from the reaction to make the equilibrium go forward. If there is water left in the flask, it can cause the equilibrium to go back towards the starting materials, or at least stop the progression of the reaction. See the intro page for the mechanism (its just the inverse of the one shown… they can either start from the final product or from the step after the
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Unformatted text preview: hemiacetal). 2. Draw the TLC you’d expect to see when monitoring your reaction, as is instructed in your lab manual. Assume it has not yet gone to completion. (2 points) 2 3. Why do you add an aqueous solution of 10% Na 2 CO 3 to your solution at the end of the reaction? Draw the acid-base reaction that occurs. (2 points) It is to get the acid out of the organic phase: 4. Draw any cyclic sugar (carbohydrate) and identify its acetal or hemi-acetal linkage. (1 point) 5. Draw the 2 products formed (in nearly equal quantities) during the protection of the following diol. Make sure to represent clearly your stereochemistry. (2 point) OH OH i-Pr H + Ph O H i-Pr O O Ph H i-Pr O O H Ph + 1 point for having the right product, no matter what the stereochemistry is. 1 point for the correct stereochemistry of both diastereoisomers....
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