Click here for a copy of the mechanism sheet used in lecture today.

Rules of the Day 4-14-08

1. You must be familiar with the atomic orbitals involved with delocalized pi systems, including aromaticity. For example, you should be able to describe the pyridine molecule in terms of: overlap of sp2 hybrid orbitals to make the sigma bonds of the ring, overlap of 2p orbitals to make the pi system, and the fact that the lone pair on N is in an sp2 hybridzed orbital.

2. Atoms with a positive charge, a negative charge or an unpaired electron are all highly stabilized by resonance when attached directly to an aromatic ring. Phenols are extra acidic because the phenoxide anion is resonance stabilized. It is important that you can draw all of the contributing resonance forms of the phenoxide anion, and thus you understand why the negative charge is on the ortho and para positions.

3. As the result of the benzyl radical stability, it is easy to carry out free radical halogenation of the benzyl position using X2 and light or heat.

4. Alkyl groups on benzene rings are oxidized all the way to carboxylic acids using Na2Cr2O7/H2SO4 (H2CrO4) as long as there is at least one benzylic hydrogen atom on that alkyl group.

Homework: Finish working on homework Set 9. Click here to download a copy. Read 22.1-22.2