Problems Set - Meeting #6

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

1. Make sure that you understand the procedures carried out in the lab very well. This does not mean that you have to memorize the exact amounts of chemicals added, but why certain steps are performed and how they are performed correctly (see lecture 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 self-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, which most students will miss entirely if they are just memorizing the answers.

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. If you fail the exam, it will be irrelevant on how you performed in the in-lab portion. This also means that you will have to repeat the entire course again including the in-lab part.

4. Finally, make sure that you put 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.

5. The instructor will not sign any late drops forms (dark red form) after week 7. Unexcused absense in the lab and/or the final exam or lack of turning in all assignments/reports by the day the final exam is administered will result in an automatic "F"-grade for the course.

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.

1. 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 one hour prior to the in-lab meeting 6. (Hint: In some cases more than one answer is correct!) Even though you can take the quiz until one hour prior to meeting 6 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 (Virtual 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 .

2. Theory of Diels-Alder Reactions

a. How many electrons are involved in a "normal" Diels-Alder reaction?

b. Why is it important that the diene can assume the s-cis conformation in the reaction?

c. In which way do acceptor groups in the dienophile influence the Diels-Alder reaction?

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

a. What is the diene on this reaction?

b. Benzyne is the dienophile in the reaction. How is it obtained? Show a balanced chemical equation.

c. 1,2-Dimethoxyethane is used as solvent in the reaction. Rationalize the choice. What is the structure of this compound?

d. The reaction is carried out in a 10 mL round-bottomed flask.Why?

e. Which observations should the student make during the course of the reaction if the reaction went according to plan?

f. A student attempts to recrystallize the crude product from methanol. What would he observe?

g. The final product only exhibits a low number of peaks in the IR spectrum, most of which are fairly weak. Rationalize this observation.

h. The product exhibits a double melting point. What does this mean and how can this phenomenon be explained?

i. A student observes the following yields:

Determine the overall yield for the conversion of benzaldehyde into tetraphenylnaphthalene assuming that the intermediates were completely used up and that they were the limiting reagent in each subsequent reaction.