Problems Set - Meeting #6

General:

1. Since there were several inquiries about how to study for the final exam, here are a few pointers (from teh instructor's point of view):

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 because this usually causes a lot of confusion.

2. The exams in the exam reader (the light green thing that you paid for when you bought in the package and have most likely not looked at up to this point) should give you a good idea about the subjects that you are expected to master by the end of this course. Use the exams as diagnostic and practice tool. 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 will 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.

2. After reviewing the TLC chapter in the reader, take the online quiz

(http://bacher.chem.ucla.edu/TakeQuiz/?id=d3d9446802a44259755d38e6d163e820). The quiz is worth 10 points, and has to be taken until 1 hour prior to the in-lab meeting during week 6. (Hint: In some cases more than one answer is correct!) Even though you can take the quiz until one hour prior to meeting 2 of your section, you should not delay taking it since there might be some problems with the server. There seem to be problems with some MAC systems as well. After you submit the answers, your score should appear on your screen. If this does not happen, you will have to retake the quiz. (There will not be any possibility to retake the quiz weeks later!).

In order to take the quiz, you have to go through a UCLA ICP address. This means that you either have to use your Bruin-Online account or go through the VPN (Vitual Private Network, software can be found here: http://www.bol.ucla.edu/services/vpn/) to have this UCLA ICP address. To log in, use your last name and your student ID. If you are experiencing problems, contact the instructor via email and include your full name (indicated which one is your last name), your student ID and section .

And now to something entirely different.....the homework questions:

3. Theory of Diels-Alder Reactions

a. Which of the following compounds can be used as reactants of a Diels-Alder reaction: benzene, benzyne, benzil and benzoin? Explain.

b. How many electrons are required to carry out a Diels-Alder reaction under "normal" conditions? Explain.

c. The reaction is considered regioselective. What does this mean? Give an example other than the one used in the reader.

d. Why does the reaction of butadiene with ethene require a higher temperature than the reaction of 2,3-dimethylbutadiene with a 3-buten-2-one.

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

a. How is benzyne obtained in the reaction? Which function does benzyne have in the reaction?

b. Why is 1,2-dimethoxyethane used as solvent here?

c. The reaction is carried out in a 10 mL round-bottomed flask. This seems to be rather large for the amount of solvent used. Rationalize this choice.

d. The reaction mixture is poured into a mixture of methanol and water. Explain briefly.

e. The crude product dissolves and precipitates fairly slowly during the recrystallization process. Why?

f. Why is it important to dissolve the entire sample before diluting the solution for UV-Vis spectroscopy?