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Unformatted text preview: 1 CHM 2526 FINAL EXAM – ANSWER KEY Professor: Dr. Louis Barriault Date: December 14, 1999 Time: 3 hours Name: Student #: 1. In silica chromatography, alcohols are usually more polar than ketones. There are certain cases, however, where alcohols are less polar than ketones. For instance, A has a larger R f than B . Briefly explain. (5 pts) OH O A B A is less polar because the tertiary alcohol is fairly hindered. It therefore interacts less with the silica (makes less hydrogen bonds than if it was less hindered). 2. Using a flowchart, clearly describe a method to separate the following mixtures (chromatography not allowed). (12 pts) Note. A separation is not a purification. NH 2 OH A) Add aqueous HCl and an organic solvent (Et 2 O or ethyl acetate) organic phase + NH 3 R Cl aqueous phase Add aqueous NaOH and an organic solvent NH 2 R organic phase + NaCl aqueous phase NH 2 Dry; evaporate the solvent Dry; evaporate the solvent OH OH 2 B) OH OH + + NaCl O Add aqueous NaHCO 3 (weak base) in water organic phase aqueous phase Phenol PhCO 2 Na Dry; evaporate solvent + NaCl aqueous phase Add dilute aqueous HCl and an organic solvent organic phase PhCO 2 H CO 2 H Dry; evaporate solvent PhCO 2 H + PhOH Add organic solvent (Et 2 O or ethyl acetate) and water. Discard aqueous phase to remove NaCl. OH In organic phase 3. You are performing a bromination of cis-1,2-diphenylethylene, and you obtain 3 products. Explain the formation of C (about 30% of the mixture) (5 pts)....
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This note was uploaded on 01/25/2011 for the course MAT 1330 taught by Professor Dumitriscu during the Spring '08 term at University of Ottawa.
- Spring '08