Problems Set - Meeting #3

Announcements (Please carefully because you will held fully responsible):

1. Safety

a. The student has to come properly dressed to the lab. Long pants and closed-toe shoes are mandatory. The feet have to be completely covered. A flame-resistant lab coat of proper size has to be worn all at times in the lab. The lab coat has to be buttoned up as well. In addition, goggles have to be worn at all times to protect the student's eyes. Repeated failure to follow these rules will lead to a dismissal from the course.

b. All experiments have to be carried out in the hood. This also applies to vacuum filtration, extractions, etc. In addition, the experiments are to be carried out in the scale given in the reader. Upscaling is strictly prohibited. Anybody doing so will be reported to the Dean of Students for cheating. There are reasons why the experiments are carried out in the scale given in your course reader (safety, economic, time scale, etc.).

c. When disposing the syringe needles in the sharps container, the caps have to be removed.

2. Experimental

a. The condenser with the cooling loop (containing propylene glycol) is used for the reflux.

b. It is very important that the reaction mixture is properly refluxed, which implies that the mixture boils and the reflux ring in the lower third of the condenser is observed.

c. If the reaction afforded a very fine precipitate, a Büchner funnel should be used for filtration.

d. The optical rotation should be acquired during meeting 4 because the polarimeter will not be available during week 3 (meeting 5 and meeting 6).

3. Formal Report

Make sure that you make progress on your formal report as well in terms of literature search and writing the parts that you completed already in the lab. The draft for the report will be due by January 22, 2016 at 4:30 pm.

4. Quiz 1

The first quiz will be administered in lecture on January 12, 2016 at 9 am (covering the introduction to asymmetric synthesis and the resolution step). It is the student's responsibility to arrive on time which means that you have to be seated by 8:55 am. Late arrivals (even if it is only one second) will not be allowed to take the quiz, which means that you will receive an automatic zero score for the quiz. If you do not place your name on the quiz to assume authorship during the alloted time, you will receive a zero score as well! You cannot add the name after time was called because this is considered cheating. It is also not allowed to start writing (including writing down your name on the quiz) until you are allowed to do so by the instructor. Failure to follow these rules will result in an immediate dismissal from the quiz resulting in a zero score. Spelling errors will cause in an 0.5-point penalty per incident. Carbon and nitrogen atoms with five or more valences receive a 2 point deduction per incident, so do other atoms that exceed the maximum number of valences.

5. Lecture materials

a. In case you did not get the emails that were sent out to the class, the lecture slides are posted here here. Make sure that you look at them before you attend the lecture.

b. The podcast can usually be found on Bruincast. The waitlisted students should be able to access this information later this week or early next week (depending on when they are being officially enrolled in the course).

c. Students that did not take Chem 30AL and Chem 30BL should review the basic techniques asap. Several videos covering recrystallization, extractions, pulling capillaries for TLC, etc. can be found on the Chem 30BL course website.

5. The question below are due with your prelab on January 12, 2016 or January 13, 2016 depending on when your section meets.

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.

Referring to the Synthesis and Characterization of the Jacobsen Ligand, answer the following questions.

a. Why is it important to use at least two equivalents of potassium carbonate in the initial stage of the reaction?

b. The reaction in a. is carried out in water. Rationalize the choice.

c. Why is 95 % ethanol added after the dissolution of the tartrate salt?

d. Upon completion of the reaction, water is added to the hot reaction mixture. Rationalize this step.

e. Which solvent is used for the extraction step in literature? Which solvent is used to dissolve the crude product to perform the extraction in the lab? Rationalize the choice.

f. Why is it important to minimize the amount of drying agent?

g. The literature reports a signal at δ=8.35 ppm in the ¹H-NMR spectrum of the ligand among many other signals. Explain briefly how this signal looks like and rationalize its location.

h. The student acquires the optical rotation for the ligand. He dissolves 35.0 mg in 7.00 mL of hexane and determines the optical rotation for this sample to be α= -1.51^o. Determine the optical purity of the sample considering that the specific optical rotation of the (R,R)-enantiomer of the ligand is [α]= -315^o. Show your work. Discuss the result.