updated last Mon, Aug 15, 2005

Week 4 Problem Set - 30BL (Turn in your computer assignment during week 5)


PART I. (Reduction of Camphor)

This assignment is to be completed in the YH1054 (the lab will be open for most part) computing labs during the lab period (or afterwards if you don't complete it in the allotted time).

1. Optimize the above structural geometry of borneol, camphor and isoborneol. (see below instructions). Compare the heat of formation of borneol and isoborneol. Which one is thermodynamically more stable? How can you rationalize the differences?

2. Determine the dipol moment for borneol, camphor and isoborneol (see below instructions). In the GC spectrum, camphor has the shortest retention time. Borneol elutes in the end. Can you rationalize the GC results based on the calculated dipole moment of these compounds? (Note: The GC column used is an HP-5 column, which is relatively non-polar.)


Instructions:


See these Helpful Hints for manipulating structures!

Note:

1 au = 1 hartree = 627.5 kcal/mol
1 eV = 23.06 kcal/mol
1 hartree = 27.21 eV
1 Ångstrom = 1.889762 atomic units = 10-8 cm

PART II. (Aldol Condensation)

1. Calculate the dipole moment for dihedral angles: 0 through 180 degrees in 15 degree increments. Plot the dipole moment of benzil vs. the dihedral angle.

Newman Projection of Benzil

Instructions:

Part III: Phase Transfer Oxidation (due in prelab)

1. A student reacts 2,4,4-Trimethyl-1-pentanol with concentrated sulfuric acid at 180 oC. After drying and a second distillation, he obtains a GC spectrum for the final product on an HP-5 column.

a. Assuming that he maintain a temperature of 120 oC throughout the run, how many peaks will he observe? (Hint: You might want to think about the product(s) of the reaction?)

b. What (if any) will change if he starts at 70 oC and ramps up the temperature to 100 oC within 10 minutes?

c. Assuming that he observes three peaks with areas of 200, 300 and 500 units, respectively, what is the relative composition of the mixture?

2. A separatory funnel is used this week. Answer the following questions.

a. Why is the separatory funnel used here?

b. Why does the separatory funnel often have a 'pear shape' ?

c. Which tests should be performed prior to using the separatory funnel?

d. Why is the stopper removed on top when the solution is drained?

3. Referring to the reaction carried out in the lab, answer the following questions.

a. How could you test if the reaction is completed before you work it up? (Hint: Which reagent is limiting here?)

b. Why is a sodium phosphate solution added to the reaction mixture?

c. Why do you place the beaker with the solution under the hood when removing the solvent?

d. Outline a brief procedure how to set-up and and perform the column chromatography step.

e. Which precautions have to be taken when removing the solvent after the chromatography step?