General Announcement (Please read!)

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. A question generally should demonstrate the student's ability to analyze the problem and be as specific as possible in his/her inquiry.

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 reaction carried out in the lab, answer the following questions. Show pertinent equations where appropriate.

a. What is the difference between absolute and 95% ethanol? Which one is used at which point in the reaction and why?

b. Why are the methylene protons of dibenzylketone more acidic than the once on 1,3-diphenylpropane? What are the implications of this observation? Show pertinent equations.

c. Which observation(s) during the course of the reaction indicate the progress of reaction?

d. A student attempts to recrystallize the crude product from a mixture of hexane and toluene (1:4). What would he observe?

e. Why is it important that the solution cools down slowly after dissolving the sample?

2. A student has 360 mg of a crude product X. If the solubility of X is 60 mg/mL at 80 ^oC, 20 mg at 20 ^oC and 10 mg/mL at 0 ^oC, how many grams of the product would he recover if he conducts the recrystallization properly?

3. The student obtains the TLC for his final product.

stationary phase: silica mobile phase: ethyl acetate:petroleum ether (1:1)

a. What can be concluded about the relative polarity of the compounds?

b.What can be said about the purity of the final product?

c. What would change if the student would use i) only petroleum ether ii) only ethyl acetate as the solvent?

d. Describe briefly how the R_f-value of a compound can be determined from the TLC plate above.

4. A student has to obtain the UV-Vis spectrum for compound W. The literature reports the following peaks: 218 (4500), 400 (2000), 650 (500). He uses a methacrylate cuvette and ethanol as the solvent. (Note: The number in parathesis are the molar extinction coefficients)

a. Which concentration(s) should he use in order to determine the molar extinction coefficient for all peaks that he will be able to observe in his measurement?

b. Which color does the product have?

c. Why is denatured alcohol not a good solvent for measurements in the UV range?