Problems Set - Meeting #6

General:

1. 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 green 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.

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.

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

1. Theory of Diels-Alder Reactions

a. What are the "key components" of a Diels-Alder reaction?

b. Why do acceptor groups often increase the rate of reaction? When is this true?

c. Why are most Diels-Alder reactions exothermic?

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

a. What is the function of benzyne in the reaction and how is it obtained?

b. A student decided to use toluene instead of 1,2-dimethoxyethane. What would he observe?

c. How does the student know that the reaction is completed?

d. Why is the reaction mixture poured in a mixture of water and methanol and not only water?

e. Which problems is the experimenter going to face during the recrystallization?

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

a. Many simple organic compounds are colorless, while more complicated organic molecules exbibit a broad variety of colors. How can this observation be rationalized.

b. Solvents like absolute ethanol and hexane are generally good solvents to acquire UV-Vis spectra. Explain briefly why. What are the limitations?

b. How does one figure out which concentration should be used to acquire a UV-Vis spectrum?

c. A student tries acquire the UV-Vis spectrum of TPCP. Even though his stock solution is dark purple, only part of the compound dissolved. Afterwards, he dilutes the sample twice ten-fold. What would he observe?

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