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Problems Set #5
ATTN: answers to the below questions are due at the start of your lab period of Meeting 6; these answers should be part of your pre-lab write-up.
Announcements (Please carefully because you will held fully responsible):
1. Quiz 2
The second quiz will be administered on Tuesday, April 13, 2010 at 12:00 pm covering safety, the ligand and catalyst synthesis and characterization. Bring a ruler, non-graphing calculator and blue or black pen with you. Please make sure that you arrive on time (this means that you should be seated by 11:55 am!!!). Late arrivals will not be allowed to take the quiz!!! The student is only allowed to write in the time slot permitted. This also applies to writing down the name. Failure to do so will be regarded as cheating.
2. In-lab work
Starting this week, students will only be allowed to attend their own lab section. This means that you have to be better prepared when you come to the lab to get the work done in the allotted time, which is easily possible if you know what you understand what you are doing. If there are questions, you should ask them during office hours!
3. No Data-sharing
There is no data sharing unless permitted by the instructor. Everybody has to acquire her/his own spectra and data i.e. melting point, optical rotation. Students who share data will be reported to the Dean of Students since this is be considered cheating. This also means that the student name has to be denoted on the FTIR spectrum when the spectrum is acquired.
4. Draft for report
Make sure that you make progress on your formal report as well in terms of literature research and writing the parts that you completed already in the lab. The draft version of paper is due on April 23, 2010 at 4:30 pm. The draft version is worth 15 points, the final paper 45 points. For more information what the draft is supposed to contain see here. Late submission will receive less credit. The more of your work you submit in the draft, the more feedback you will get, which will beneficial for the final version. We will try to return the reports by Monday, April 26, 2010. The final version of the paper will be due by May 7, 2010.
5. Podcast and Anser Keys
a. The lecture is podcasted. The file is uploaded in the afternoon or the following day onto the bruincast website.
b. The instructor posts the answer keys for the homework assignments on the website as well (follow Chem 30CL link, weekly assignments)
6. Safety
a. Make sure to be careful when you handle glassware. This applies to the use during a reaction as well as the cleaning. Broken glassware can cause very deep cuts which have often to be stitched up. If chemicals get into the open wound, the wound have to be specially treated and the healing process takes often more time as well.
b. It has come to the attention of the instructor that students dump acetone down the sink. This is entirely unacceptable. If a student will be caught doing this, s/he will receive an automatic zero for the entire lab meeting. Repeat offenders will be dismissed from the course due to safety issues.
7. Experimental changes
a. Ethyl acetate will be used instead of dichloromethane during for the epoxidation reaction.
b. A mixture of ethyl acetate and hexane (1:3) should be used as the initial mixture for the TLC.
And now to the fun part...the prelab questions that are due in your prelab for April 13 and April 14, 2010 (=meeting 5):
1. Referring to the catalyst design, answer the following questions.
a. What is the exact function of the tert.-butyl groups in the catalyst? What would happen if the groups in the 3 and 3'-positions were replaced by larger groups i.e. naphthalene rings?
b. What is the function of the cyclohexane part in the catalyst?
c. What is the active species in the epoxidation? Provide a structure for this species. Describe the structure.
d. In lecture it was discussed that the e.e.-value for styrenes are about 50% under the conditions chosen in the experiment. Explain briefly why.
2. Referring to the epoxidation reaction carried out in the lab, answer the following questions.
a. The reaction carried out in a biphasic system. What does this mean? What does this means for the experiment?
b. Why is it imperative to use a buffer in this reaction?
c. A student uses 5 mmol of the alkene for the epoxidation. How many grams of catalyst should he use if he is asked to use 10mol% of the catalyst?
d.Why is important to work the reaction mixture up immediately after the reaction was completed?
e. The procedure asks to find a mobile phase that results in a Rf-value of 0.4 for the epoxide and a Rf-value of 0.8 for the alkene. Why?
f. The epoxide is visualized using ceric staining. Explain briefly how this method works. Which compounds can be visualized with this technique?
g. How is the crude epoxide stored?