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 pink thing that you paid for when you bought in the package and 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 quarters just did not spent enough time to review the material and tried to "wing" the exam, not very successfully as mentioned earlier in the quarter already.

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.....the homework questions:

1. Theory of Diels-Alder Reactions

a. One important point for the Diels-Alder reaction to occur is that the diene has to be in s-cis conformation. Explain briefly.

b. Diels-Alder reactions between electron-poor dienophiles and electron-rich dienes are generally very fast. Rationalize this observation and provide and example other than the one shown in the reader.

c. Which four criteria make a compound aromatic? In which way does this apply to "normal" Diels-Alder reactions?

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

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

b. Why is 1,2-dimethoxyethane used in the reaction?

c. Which observation(s) will the experimenter make during the reaction?

d. After the reaction mixture is cooled to room temperature, the mixture is poured in a mixture of water and methanol. Why?

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

f. Most of the students will observe a double-melting point. How is this double-melting point obtained and why is it observed?

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

a. Why is methanol used as solvent for the UV-Vis spectrum even though the compound does not dissolve too well in there?

b. Which concentration is needed for the UV-Vis characterization of the TPN?

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

d. Which information should be reported in the postlab write-up from the UV-Vis spectrum?