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 April 18, 2006 at 12 pm. Please make sure that you show up on time.
3. The next workshop (4/17/2006) will cover infrared spectroscopy and extraction theory. Based on my last week's observation in the labs, I highly recommend that some of you try to show up there to refresh the knowledge in these topics.
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. Arginine, an amino acid that serves as precursor for the NO production in the human body, is found in nuts, sunflower seeds, sesame seeds, chocolate, brown rice, and protein rich foods. A student isolates a sample of arginine from one of these natural sources. He observes an optical rotation of a=(+1.48o) for a solution of 0.350 g in 5.00 mL of 6 N HCl in a 10 cm polarimetry cell.
a. Determine the optical purity of the sample and the absolute stereochemistry (R/S and D/L) of the arginine isolated.
b. Would the optical rotation change if the solvent would be changed to 1M NaOH?
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. Could one use potassium hydrogencarbonate instead? Show a balanced equation and explain.
b. Why is it important to use a slight excess of the aldehyde in the reaction?
c. The ligand exhibits a bright yellow color. Rationalize this observation.
d. Some of the students will use a rotavap to remove the solvent from the ligand. Which advantage does this technique have?
e. The ligand still possesses two phenolic functions. However, the infrared spectrum does not exhibit the characteristic broad OH peak at 3200-3400 cm-1. Rationalize this observation.