1. General

Review the following topics: recrystallization theory, vacuum filtration, ¹³C-NMR spectroscopy, UV-Vis spectroscopy

2. Experiment

Safety note:

Isopentyl nitrite (isoamyl nitrite, IPN) is a powerful heart stimulant. Do not spill it on the bench and avoid inhaling in the vapors. The compound have to be handled under the hood and containers kept closed as much as possible. Place the the reaction setup as close as possible to the hood at your bench.

The reaction has to be carried out in a 10 mL round-bottomed flask. Why?

It is important that both solids are dissolved in 1,2-dimethoxyethane before adding the isopentyl nitrite slowly. Why?

The color change from purple to orange yellow occurs often gradually. If the solution remains remains purple, add 1-2 drops of pure isopentyl nitrite first and reflux for five more minutes. If this does not cause the color to change, add ~10 mg of the acid dissolved in ~0.5 mL of 1,2-dimethoxyethane.

The final product tends to dissolve and precipitate very slowly during the recrystallization process. Be patient when you add additional solvent to dissolve it. It might be a good idea to place a watch glass with ice on top of the Erlenmeyer flask. Why?

If the crude does not dissove completely, decant the solution and use some fresh, hot solvent to dissolve the rest. If the compound does not dissolve, discard it, otherwise combine this solution with the first solution.

3. Things to think about

a. How would the ¹³C{¹H}-NMR spectrum of 1,2,3,4-tetraphenylnaphthalene (TPN) change if the temperature is lowered to T= -78 ^oC during the measurement?
b. Why is tetraphenylcyclopentadienone dark purple in color while tetraphenylnaphthalene is white?
c. How can the double melting point of TPN be explained?
d. How do you calculate the ε-value for a given wavelength? What does the ε-value represent anyway?
e. How many ε-values should the student report in the postlab report?
f. Why is isopropanol used as a solvent for the recrystallization?
g. Why is it impossible to isolate pure benzyne?