Chem 242 @ Dickinson

Start of Carboxylic Acids

Today we started talking about carboxylic acids. Most of the discussion was centered around factors that control the acidity of the carboxylic acid. There were two major ways to look at this: Induction and resonance. Induction was defined as a "through-space interaction" in which electron-withdrawing groups on carbons near to the carboxyl fragment could induce a partial positive charge on a carbon atom, which would in turn "drag" the negative charge of the conjugate base towards itself, thus increasing the volume of space occupied by the charge. This increases the stability of the conjugate base, leading to increased acidity of the carboxylic acid itself. Substituted benzoic acids were used to demonstrate how resonance could play a role; electron-withdrawing groups placed a partial positive charge next to the carboxylate and therefore stabilized the conjugate base (thereby increasing the acidity of the acid). Electron donating groups had the opposite effect.

The first 20 minutes of class dealt with finishing up the enamine reaction started last Friday. We showed how to go "backwards" and do a hydrolysis of the enamine, ending up with the carbonyl compound and starting secondary amine. It will be important to be able to show mechanisms in both directions.

posted by DCChem @ 10:09 AM