Problems Set (Meeting 9)

General Announcements

1. Quiz 4

Quiz 4 will be administered on Tuesday, February 3, 2015 at 9 am covering the gas chromatography and the spectroscopy of epoxides (MS, NMR, etc.). Otherwise, you will not be allowed to take the quiz. Make sure to bring a ruler and a non-graphing calculator with you.

2. Lidocaine Project

a. The postlab report for the lidocaine project has to be written in the lab notebook and submitted to the teaching assistant. The due dates are February 12, 2015 or February 13, 2015 in your regular lab section. The report has to be written in the lab notebook and is worth 15 points.

3. Grignard Project

a. The Grignard project will start on February 10, 2015.

b.The instructor will provide an in-lab demonstration of the Grignard setup (setup, heating, etc.) on February 9, 2015 at 4:00 pm in YH 6086. Attendance in this demonstration is voluntary (no credit) and is highly advisable for students that feel intimidated by the larger setup. Part of the demonstation will already discussed in lecture prior to this in-lab demo, but certain aspects like heating cannot be shown in the lecture.

4. Research project (Week 9)

a. Please look start looking for a partner for the Ferrocene project. Your partner should be in a different time slot than yourself i.e., if you are in the T/R afternoon section, try to find somebody in the W/F afternoon section. This way nobody has to put in additional time outside their regular schedule, which means that each group has four lab meetings to complete the project. We have to avoid as much as possible to have the entire class running around in the lab (Safety!).

Questions (due on 2/3/2015 or 2/4/2015)

1. Referring to the conversion of a-chloro-2,6-dimethylacetanilide to lidocaine (step 3), answer the following questions. Show pertinent balanced chemical equations.

a. Why is it important that the anilide is dry?

b. The reaction uses three equivalents of diethylamine. Rationalize the choice.

c. Assuming that the student started with 1.00 g of the anilide, which observations should the student make during the course of the reaction? Rationalize this observation.

d. The reaction mixture is refluxed. Which observations should the student make?

e. After the extraction with water, the organic layer is extracted several times with diluted hydrochloric acid. In which layer is the product afterwards? In which form?

f. The solution obtained in e. is reacted with concentrated potassium hydroxide solution. Provide a balanced equation for this reaction.

g. The student has to submit a sample for NMR analysis. Which solvent is used here? What is the desirable concentration?

2. Spartan assignment (Part 4 of the Project, can be done ooutside the lab or during meeting 10)

The goal of this exercise is to determine the barrier of rotation of an amide bond. To this end, the energy of the N,N-dimethylacetamide is determined for dihedral angles from 0 to 360 degrees.

Instructions:

1. After drawing the molecule in Spartan 2010, click on Constrain Dihedral angle tool, in the tool bar.

2. Select the atoms shown below in the specific sequence C..N..C..O. A pink line will appear between N and C₂. This will define two planes C₁N₁C₂ and NC₂O, which are going to be rotated towards each other in this part.

3. Click on the lock tool, , in the bottom right corner so that it looks like this,

4. Set the dihedral angle to 0 and hit the ENTER key.

5. Click on the minimize tool, , and wait for the operation to complete

6. Click on the minimize tool, , a second time and wait for the operation to complete.

7. Select Calculations from the Setup menu. The following window should appear. Select the options shown.

Pick Hartree-Fock (6-31**) in vacuum.

8. Make sure the are checked. The Total Charge is Neutral and the Multiplicity is Singlet. All other boxes should be unchecked.

9. Click OK to close the window. Save the file with a unique name (i.e., DMF_0 degrees)

10. Select Submit from Setup menu. When the calculation is completed you will be notified.

11. Under the Display menu, select Properties.

12. A window should appear (the values in this example should differ from yours). If there are no values in the window then you need to double click on the molecule.

The energy of the molecule is recorded (here: -247.002139 au).

13. Repeat this for all angles between 0 and 360 degree in 10 degree increments. (Hint: Just click on the pink bond and change the value in the box. Do not define a new constraint at this point because this will confuse the program completely.)

14. Using EXCEL, plot the energy of N,N-dimethylformamide vs. the dihedral angle (use MS Excel, XY Scatter plot). Rationalize the observed trends. Determine the barrier of rotation from the graph (1 au = 2625.5 kJ). How well does the calculated value match the data provided in the course reader?

15. Include the graph and the discussion of the data into the postlab report for the lidocaine project.