last updated Tuesday, October 18, 2005

Problems Set #7

General announcements:

1. The draft version for the paper is due on Friday, October 28, 2004 at 5 pm.

2. The next quiz will be administered on October 24, 2005 at 12 pm covering the rest of the epoxidation project.

ATTN: answers to the below questions are due at the start of your lab period of Meeting 7; these answers should be part of your pre-lab write-up.

1. The last step of the epoxidation involves flash chromatography.

a. What is the purpose of this step?

b. Why and where is sand used to prepare the column?

c. Why is the stationary phase treated with a 1% NEt3 solution before the sample is applied?

d. How do you find out which part of the eluent contains the desired epoxide?

2. NMR spectroscopy

a. Which solvent is used to acquire the NMR spectra of the final product? Why?

b. What is the 'proper' labeling for the NMR tube?

3. GC/MS spectrometry

a. A student acquires the GC/MS spectrum for his epoxide using a modified b-cyclodextrin column and a temperature of 90 oC throughout the run. One peak at t(r)=15.6 min has a absolute area of 150 units, while another one at t(r)=15.8 min only has 40 units. Both peaks show identical fragmentation in the mass spectrum and a [M]+-peak of 168. In addition, a peak is observed at m/z=170, which is about a third of the intensity than the [M]+-peak. The peak at m/z=169 is about 10% of the peak at 168. Which conclusions can the student draw from this data?

b. What is the "proper procedure" to obtain the GC spectrum?