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Problems Set #7
General announcements:
1. The draft version for the paper is due on Friday, October 29, 2004 at 5 pm in YH1217.
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. A student acquires the GC/MS spectrum for his epoxide using a modified b-cyclodextrin column. One peak at t(r)=18.2 min has a absolute area of 150 units, while another one at t(r)=18.5 min only has 50 units. Both peaks show identical fragmentation in the mass spectrum and a [M]+-peak of 198. In addition, a peak is observed at 200 amu, which is about same intensity than the [M]+-peak.
a. Which conclusions can the student draw from this data?
b. Why is the modified b-cyclodextrin column used here and not a HP-5 column?
2. The last step of the epoxidation involves a flash-chromatography.
a. What is the purpose of this step?
b. Why is sand used to prepare the column?
c. Silica is used as a stationary phase in this step. Why is this be a problem in this step? How can you eliminate this problem?
d. How do you find out which part of the eluent contains the desired epoxide?
3. Which solvent is used to acquire the NMR spectrum of the final product?