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 quiz will be administered on Tuesday, January 23, 2007 at 12 pm covering the resolution step and the ligand synthesis. 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. Tyrosine was first discovered in 1846 by German chemist Justus von Liebig in cheese. It is one of the 20 amino acids that are used by cells to synthesize proteins and can be converted to DOPA by tyrosine hydroxylase. A student isolates Tyrosine from a natural source. He observes an optical rotation of a=(-1.10o) for a solution of 1.0 g in 5 mL of water in a 5 cm polarimetry cell. Determine the optical purity of the sample and the absolute stereochemistry (R/S and D/L) of the tyrosine isolated.
2. Referring to the synthesis and characterization of the Jacobsen ligand, answer the following questions.
a. Potassium carbonate and the ammonium tartrate salt are dissolved in water. Provide a balanced chemical equation for this reaction. Why is it unwise to use potassium hydroxide for this reaction?
b. The students adds the aldehyde solution to the solution prepared in a. What should he observe?
c. After the reaction is completed, water is added before the mixture is allowed to cool down. Why?
d. Despite possessing two phenolic functions, the ligand does not show the characteristic hydroxyl peak in the range between 3200-3500 cm-1. Rationalize this observation.
e. Which solvent is used to acquire the optical rotation for the ligand? What is the expected value for the specific optical rotation of the ligand?
f. What does the subscript "D" stand for in the refractive index and the specific optical rotation data?