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 sodium hydroxide in this reaction? Show pertinent chemical equations.

b. Why is it important that the reaction mixture is homogeneous before storing it?

c. Benzaldehyde is easily oxidized in air. Which problem does this pose for this reaction?

d. A student starts off with 0.30 g of thiamine hydrochloride and 1 mL of 0.20 N sodium hydroxide solution. Afterwards, he adds 1.50 mL of benzaldehyde to his solution. In the end he isolates 1.30 g of benzoin. Determine the yield for the reaction. Show your calculations.

e. At room temperature, benzaldehyde is a liquid while benzoin is a solid. Rationalize this observation.

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 the proper sized filter paper in this step?

c. Why has the filter flask to be clamped during the filtration?

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

a. Student A forgets to heat the mixture during the reaction. Which problem is he going to face?

b. If the reaction mixture was heated, it usually turns black or dark blue or dark green. Rationalize this observation.

c. Student B follows the protocol for the reaction and obtains two layers after the reaction. Explain briefly how he should isolate the two layers.

d. What is the function of the saturated sodium chloride solution used during the work-up?

e. How are you going to acquire the IR spectrum for the final product in the lab? Outline a brief procedure.

4. 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.

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