Problems Set - Meeting #4
Announcements:
1. Make sure that you make progress on your formal report as well in terms of literature search and writing the parts that you completed already in the lab.
2. The second quiz will be administered on Tuesday, April 15, 2008 at 12 pm covering the resolution step and the ligand synthesis. Please make sure that you show up on time. If you arrive late, you will not be allowed to take the quiz.
ATTN: answers to the below questions are due at the start of your lab period; these answers should be part of your pre-lab write-up.
1. Aspartame is the name for an artificial, non-saccharide sweetener, aspartyl-phenylalanine-1-methyl ester; i.e., a methyl ester of the dipeptide of the amino acids aspartic acid and phenylalanine. Phenylalanine itself cannot be made by animals, which have to obtain it from their diet. It is produced by plants and most microorganisms from prephenate. A student isolates what he believes to be phenylalanine from a plant. He dissolves 1.00 g of the compound in 10.0 mL of water. The resulting solution exhibits an optical rotation of a= -3.15o in a 10 cm polarimetry cell. Determine the optical purity of the sample. Which enantiomer did he isolate?
2. Referring to the synthesis and characterization of the Jacobsen ligand, answer the following questions.
a. How many equivalents of potassium carbonate are required for the reaction? Show pertinent equation(s).
b. Why is water used in the initial part of the reaction?
c. After the initial part of the reaction (reaction of the tartrate with potassium carbonate), 95% ethanol is added. Explain why.
d. Despite the presence of two hydroxy functions in the molecule, the compound only exhibits a fairly low intensity OH peak in the IR spectrum. Explain.
e. Which solvent is used to acquire the UV-Vis spectrum for the ligand? Which concentration is appropriate here?
f. The phenolic proton shows up at d=13.6 ppm and the imine hydrogen at d=8.35 ppm. Rationalize these observations.