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 next will be administered on Tuesday January 24, 2006 at 12 pm. Please make sure that you show up on time.
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. Phenylalanine is found in fermented foods such as yogurt and miso. The alternative sweetener aspartame is a dipeptide of L-phenylalanine, as is the methyl ester, and L-aspartic acid. A student isolates a sample from a natural source. He observes an optinal rotation of a=(-0.64o) for a solution of 0.2 g in 5 mL of water in a 5 cm polarimetry cell.
a. Determine the optical purity of the sample and the absolute stereochemistry of the phenylalanine.
b. Would the optical rotation change if solvent would be changed to 1M hydrochloric acid?
2. Referring to the synthesis and characterization of the Jacobsen ligand, answer the following questions.
a. Potassium carbonate used in the initial stages of the reaction. Show a balanced equation and explain.
b. Why is alcohol added to the solution before the aldehyde is added?
c. Why does the ligand have a yellow color even though the aldehyde and the tartrate salt are white?
d. A student determines the optical rotation for his isolated ligand. Which information does he obtain from this data?
e. The signal for the OH-groups of the ligand is observed at ~13.6 ppm in the 1H-NMR spectrum. Rationalize this observation.