Rules of the Day 2-19-07

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

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

Remember there is a review session tonight from 8-10 PM in WEL 2.224!

You can see streaming video of all previous lectures this semester at http://cns.utexas.edu/lectures/classes.asp

Use login: 53760

Password: ch31on (lower case)

You will need these downloads: http://cns.utexas.edu/lectures/downloads.asp

Note the new intel based macs need a new plug-in which is now available. For more information see: http://cns.utexas.edu/lectures/

1. Keto-enol equilibration is catalyzed by acid or base. Recall that catalysis does not change the position of equilibrium, but just accelerates the rate at which equilibrium is achieved. The keto form is almost always favored! In acid, the mechanism involves protonation of the carbonyl oxygen atom, followed by loss of a proton by the a-carbon atom.

2. The alpha-hydrogens of aldehydes and ketones are relatively acidic with a pKa around 20. Deprotonated aldehydes or ketones are resonance stabilized and are called enolates. The resonance stabilization of the enolate explains the relative acidity of aldehydes/ketones.

3. Base-catalyzed keto-enol equilibrium occurs via an enolate intermediate.

4. Because acid catalysis increases the rate at which keto and enol forms equilibrate, reactions that use the enol form for reaction such as halogenation on the alpha carbon atom are accelerated in acid.

Homework: Study for the exam. You are responsible for all material covered up through last Friday's lecture. Keto-enol equiolibria will not be on the first exam. What we cover this week will be on the second exam. Read: 17.1-17.3