Week 6 Problem Set 30BL

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.

1. How many alpha hydrogens do each of the following compounds have? huh?

a.	c.
b.	d.

2. Why is absolute ethanol used as solvent for the actual reaction, and not 95% ethanol? Explain.

3. If 600 mg of a crude product is isolated, approximately how much solvent in needed for the recrystallization? How much (in gram and percentage) is recovered after the recystallization? Given: solubility of product = 30 mg/mL hot solvent, 20 mg/mL warm solvent and 5 mg/mL cold solvent.

4. The final product, tetraphenylcylcopentadienone is recrystallized from a 1:1 mixture of 95% ethanol and toluene. What would be expected if only toluene was used for the recystallization? How about methanol?

5. True or false? Explain briefly.

a. A solvent that has a steep solubility curve is a good solvent for recrystallization.

b. It is not enough to warm up the solvent gently to dissolve the compound.

c. You can add as much solvent as you like to dissolve the compound.

d. The crystals of this week's product should be rinsed with toluene.

6.

The researcher attempts to evaluate the purity of his product by TLC.

stationary phase: alumina mobile phase: hexane

a. Calculate the R_f-values for A, B and the product.

b. What can be said about the purity of the product?

c. Is the chromatogram obtained correctly?

d. What are the relative polarities of A, B and the product?