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

Rules of the Day 4-23-08

1. If there are two groups on the ring, and they predict different products, then just like in the movie, Good beats Ugly or Bad, and Ugly beats Bad. Bad always loses. Because of steric hindrance, electrophiles never add between meta substituents.

2. If an aromatic ring is loaded with electron withdrawing groups, it is no longer nucleophilic, but can react as an electrophile. In this case, strong nucleophiles can displace a halogen on an aromatic ring. We will only see one example of this very rare and special reaction, in which 2,4-dinitrofluorobenzene reacts with strong nucleophiles such as amines. This is called nucleophilic aromatic substitution, and is very, very rare compared to electrophilic aromatic substitution reactions.

3. Reacting an aromatic amine (like aniline) with NaNO2/HCl converts the NH2 group into N2+, the famous "Mr. Bill" reaction (HONO!!!!). The N2+ can be replaced by OH (using H2O), F (using HBF4), CN (using KCN and CuCN), Cl (using HCl and CuCl), Br (using HBr and CuBr), I (using KI), H (using H3PO2). The starting aromatic amine can come from reduction of a nitro aromatic (H2/Ni), and the nitro aromatic can come from nitration of an aromatic ring (HNO3, H2SO4).

Homework: Study for the exam next Thursday night.