Chem 242 @ Dickinson

A Fitting Conclusion to Amines

Today we finished amines by discussing two concepts. The first was the EAS reaction on aromatic amines; after a false start the class agreed that an amino groups should be considered to be an o,p-directing, activating substituent. The problem is that it is too activating and leads to polysubstitution. The problem can be rectified by doing some carboxylic acid derivative chemistry -- convert the amine to an amide by reacting with an anhydride or acid halide to lessen the electron donating ability of the nitrogen. Following the EAS (with only a single substitution) the amide can be hydrolyzed, regenerating the amine.

The second topic was the Sandmeyer process. Through a sequence of steps analogous to the formation of a nitronium ion, it is possible to convert HNO2 to an N=O cation. This electrophile reacts not with the ring but instead with the nitrogen of an aromatic amine; loss of water leads to a salt. A complex and not well understood substitution will take place with a number of nucleophiles, leading to removal of the nitrogen and replacement with the nucleophile.

We had a brief start to chapter 25. The subject is carbohydrates. Mostly we talked about some basic nomenclature but on Friday we will start actual chemistry. We'll need to understand the biochemist's way of drawing tetrahedral carbons (Fisher projections), so bring your models on Friday!

There is a new video of the week. If you like things blowing up in microwaves, you'll like the video.

posted by DCChem @ 10:44 AM