Problems Set - Meeting #6

General:

Since there were several inquiries about how to study for the final exam, here are a few pointers:

1. Make sure that you understand the procedures carried out in the lab well. This does not mean that you have to memorize the exact amounts added at some point, but why certain steps are performed and how they are performed correctly (see lecture, workshop and Survival Kit reader). If things are not clear to you, make sure to ask questions (TA, instructor, etc.) asap and not the day before the exam.

2. The exams in the exam reader (the light yellow thing that you paid for when you bought in the package and probably have not looked at up to this point) give you a good idea about the subjects that you are expected to master by the end of this course. However, memorizing the answers to the questions does not guarantee a higher grade in the final since there are always changes in the questions.

3. One of the most important things is to write your own prelab and postlabs, and not just copy it from a friend/roommate/etc and include your own numbers. You are not learning anything this way and most likely fail the exam miserably, which also means that you are automatically going to fail the course.

4. Finally, make sure that you take enough time aside to study for the final exam. A lot of the students that failed the exam in the past two quarters just did not spent enough time to review the material and tried to "wing" the exam.

Bottomline: If you do your own work and understand reasonably well what you are doing in the lab, you should not have any problems to get a passing (and decent) grade in the course. Please keep in mind that many of you are going on to take the MCAT, DAT, PSAT, GRE, etc. and some of the material covered in this course will show up there as well.

And now to something entirely different (anybody knows where this statement comes from?).....the homework questions :

1. Theory of Diels-Alder Reactions

a. Most Diels-Alder reaction reactions are exothermic. Explain briefly why.

b. Which feature(s) make(s) the Diels-Alder reaction stereoselective?

c. The reaction of cyclopentadiene with ethylene requires relatively high temperatures, while the reaction of cyclopentadiene with maleic anhydride can be carried out at room temperature. Show the products of the two reactions and rationalize the differences in reactivity.

d. The "endo rule" states that in many cases the endo product is formed in the reaction. Explain briefly.

2. Referring to the reaction carried out in the lab, answer the following questions.

a. How is benzyne obtained in the reaction and which function does it have? Show a balanced chemical equation.

b. The procedure suggests to carry out the reaction in 10 mL round bottom flask. Rationalize this choice.

c. Why is the function of 1,2-dimethoxyethane in the reaction? Rationalize the choice.

d. A student added all the reactants together and expects to observe a color change. Despite intense reflux, the color does not change after 10 minutes. What should he do?

e. Which problems is the experimenter facing during the recrystallization step?

3. A UV-Vis spectrum is also obtained for the compound obtained in this week's experiment.

a. Why is a plastic cuvette used instead of a test tube?

b. Which concentration is needed for the UV-Vis characterization of the TPN? How do you prepare this solution?

c. Why is it important to dissolve the entire sample before diluting the stock solution?