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Final 2000 solutions - 1 FINAL EXAM CHM 2526 Professor Dr...

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1 FINAL EXAM CHM 2526 Professor: Dr. Louis Barriault Date: December 18, 2000 Time: 3 hours ANSWER KEY 1. Using a flowchart, describe a method to separate the following mixtures. (10 points) A) NH 2 CO 2 H NH 2 H 2 N B) Add dilute aqueous HCl and an organic solvent (Et 2 O or ethyl acetate) organic phase + R NH 3 R Cl aqueous phase Add dilute aqueous NaOH and an organic solvent NH 2 R organic phase + NaCl aqueous phase NH 2 Procedure in A would also work (since RNH 2 ) Add dilute aqueous NaOH and an organic solvent organic phase aqueous phase Diamine PhCO 2 Na Dry; evaporate solvent NH 2 H 2 N + NaCl aqueous phase Add dilute aqueous HCl and an organic solvent (Et 2 O or ethyl acetate) organic phase PhCO 2 H CO 2 H Dry; evaporate solvent Dry; evaporate solvent Dry; evaporate solvent
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2 2. During the bromination of cholesterol, you added a bromine solution dropwise (red- brown colour). At first during the addition, the reaction mixture quickly returns to its original colour, but after a certain quantity of bromine is added, the red-brown colour persists. Briefly explain this observation. (5 points) At first, the double bond on cholesterol reacts with the Br 2 , therefore it’s normal for the colour to disappear. Once the colour persists, it tells us that the reaction is complete and that there is no alkene left. 3. You are given a mixture of benzyl alcohol and isopropyl benzoate. A TLC of the mixture is drawn below (eluant : 20% ethyl acetate/hexanes). (10 points) A) Calculate the R f of A et B. (4 points) Rf = distance the compound migrated from the baseline Total distance travelled by the solvent Rf (A) = 0.22 ; Rf (B) 0.61 (Measure distances using mm on the exam!) B)
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