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

Rules of the Day 4-25-08

1. 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).

2. Because of pi delocalization, an amino group attached to a benzene ring is sp2 hybridized. This explains why the DNA bases are planar!!

3. The Guanidine group is extremely basic, because the protonated form is triply resonance stabilized. This group is very common in biology. Llike amines, the guanidinium group is protonated and positively charged at neutral pH in water.

4. Pericyclic reactions are an entirely new class of reactions in which pi bonds are exchanged simultaneously for sigma bonds via an "aromatic" transition state. The Diels-Alder reaction is a great example of this kind of reaction involving a diene in the s-cis conformation reacting with a dienophile (alkene) to give a six-membered ring product. You can see this reaction on the movie page.

5. Because the Diels-Alder reaction is concerted: 1) the orientation of groups originating on the diene are determined by the s-cis conformation and 2) the configuration of the alkene (dienophile), either cis or trans, is maintained in the product.In addition (excuse the pun), carbonyl groups react in the so-called endo position "underneath" the double bonds of the diene.

6. THE KEY issue with carbohydrates is stereochemistry. The stereochemistry of carbohydrates are based on (+) D and (-) L glyceradehyde. A D-sugar has the same configuration as (+)-D-glyceraldehyde at the chiral center farthest from the carbonyl group. An L-sugar has the same configuration as (-) -L-glyceraldehyde at the chiral center farthest from the carbonyl group. The best way to see this is with Fisher projections. Click here for a molecule of the day that discusses much of this.

Homework: Here is a practice aromatic reactions and synthesis homework. Click here to download a pdf file. You will NOT turn this in, but we have posted answers, click here for the answers. It is here as a tool to get you ready for the aromatic reactions portion of the final. Click here for the last (10th) homework set. You will turn this in Friday, May 2.