General Announcement (Please read!)

1.It has come to my attention that some students are not clear about certain policies in this course. There is no such policy in this lab course which discourages students from asking questions. The reason why you are here is to learn. This should also result in questions from the the student's side, which are welcome by the teaching assistants and the instructor. However, it is expected that the student comes prepared to the lab section in order to be able to complete the experiment in a timely fashion. The majority of the questions regarding the experiment (theory and practical issues) can be answered during lecture and office hours. The question should demonstrate the student's ability to analyze the problem and be as specific as possible.

2. The miterm that I sent out on Wednesday evening is a practice midterm. You are not obligated to turn it in, but it would give you a chance to evaluate where you stand at this point in the course. The TAs and instructor will meet on 5-12-2004 at 8 am to grade the midterms that have been turned in by then. For those of you who could not read the file, here is the link to the midterm exam (PDF file).

ATTN: answers to the below questions are due at the start of your lab period; these answers should be part of your pre-lab write-up.

1. Referring to the formation of the enolate, answer the following questions.

a. Why is absolute ethanol used as solvent in this week's reaction?

b. Why is an ethanolic potassium hydroxide solution used in this step?

2. A student isolated 2.4 g of a crude product. In order to purify it, he has three solvents accessible: ethanol, dichloromethane, hexane

a. Which solvent should the student choose for recrystallization? Rationalize your choice.

b. How much of the purified compound (in g and %) would the student recover if she performs the recrystallization correctly?

c. What can be said about the polarity of the product?

3. The final product of this week's reaction is recrystallized from a mixture of 95% ethanol and toluene (1:1).

a. Why is a solvent mixture used here?

b. What would happen if only toluene is used for the recrystallization?

c. What would happen if the mixture is boiled for an extended time?

4. The researcher is given the following TLC from his assistant.

stationary phase: silica mobile phase: hexane

a. Calculate the R_f-values for all spots.

b. What can be said about the progress of the reaction?

c. Is the chromatogram correctly obtained?

5. Student C has to obtain the UV-Vis spectrum for his compound, which is non-polar. In the literature he finds the following information: 330 (2500), 400 (1500), 500 (100). He is asked to measure the range from 360-600 nm.

a. Which concentration(s) should he choose in order to determine the molar extinction coefficient for both peaks in this range?

b. Which solvent would be appropriate here?

c. Which type of cuvette should he choose?