Problem set #2 (Meeting 2)

ATTN: answers to the below questions are due at the start of meeting 2; these answers should be part of your pre-lab write-up. Show pertinent equations where appropriate.

1. Referring to the benzoin condensation, answer the following questions.

a. What is the function of the thiamine hydrochloride in the reaction?

b. What does the term "homogeneous" mean? Why is it important that the reaction mixture is homogeneous?

c. The procedure asks to use "fresh" benzaldehyde for the reaction. Explain.

d. A student starts off with 0.25 g of thiamine hydrochloride and 3 mL of 0.20 N sodium hydroxide solution. Afterwards, he adds 3.00 mL of benzaldehyde to the solution. After the work-up, he isolates 2.50 g of white crystals. Determine the yield for the reaction. Show your calculations.

e. How can he verify that the isolated solid in d. is benzoin?

2. Vacuum filtration

a. Draw a sketch for the setup used for the filtration of the benzoin and label all parts needed.

b. Why is it important to use filter paper in this step if a porcelain funnel is used?

c. Why are the crystals rinsed with ice-cold water and ice-cold 95% ethanol?

d. Why do the vacuum trap and the filter flask to be clamped?

3. Referring to the elimination reaction, answer the following questions.

a. The reaction mixture is heated to a boil and the product distilled into the Hickman head. Explain briefly why.

b. What is the function of the sodium sulfate used during the work-up? How does the student know that enough of it was added?

c. Which purpose does the second distillation serve?

d. Rationalize the boiling point differentce between cyclohexene and cyclohexanol.

e. Which qualitative test are performed to verify the presence of an C-C double bond? Show pertinent chemical equations.

4. Infrared Spectroscopy

a. How is the IR spectrum for the final product of the elimination obtained in the lab? Outline a brief procedure.

b. What are the most important changes in the IR spectrum going from cyclohexanol to cyclohexene?

5. a. Using PC Spartan 2002, perform the following calculations for the alkenes: terpinolene, limonene, a-terpinene, isoterpinolene. Make sure that all hydrogen atoms are present and there are also no extra ones either.

b. Select Calculations from the Setup menu.

The following window should appear. Select the options shown.

Verify that the Charge is Neutral and Multiplicity is Singlet. Click OK.

Select Submit from Setup menu.

Then click OK to exit dialog. Close the previous window.

Select Submit from Setup menu. When the calculation is completed you will be notified. It should not take more than one minute for the calculation to complete under normal circumstances. Make sure that you have only one window open at this point. The messages are usually displayed in the first window, and often not in the window you are working in at this point.

Under the Display menu, select Properties. Record the value for the Energy.

1. Based in the observed trends in trends in the heat of formation (=energy), which alkene is the most stable and which one is the least stable one? Can you rationalize these observations? Do the obtained data match with your expectation? If not, what is the conclusion?

2. Can you explain the product distribution observed for the elimination of water from a-terpinol (see reader page 20)?

Problems with calculations: Check here