Rules of the Day 2-22-08

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

Featured Golden Rule of Chemistry: 4. Nature hates localized charges. If a molecule must have a charge, it is better to have the charge distributed over as many atoms as possible through resonance, inductive effects, and hyperconjugation. In addition, when given the choice, it is better to have more negative charge on a more electronegative atom (e.g. O), and more positive charge on a less electronegative atom (e.g. C).

1. Fischer esterification converts a carboxylic acid into an ester using an alcohol and acid catalysis. The mechanism involves Mechanism D followed by loss of an H2O via protonation.

2. Carboxylic acids react with SOCl2 to give acid chlorides via a chlorosulfite intermediate that then reacts according to Mechanism B to give the acid chloride. This is a very valuable reaction because acid chlorides can be easily converted into other carboxylic acid derivatives.

3. The haloform reaction converts methyl ketones to carboxylates. The mechanism is the interesting part, involving enolate formation in base, three sequential replacements of H with Br, then then attack of OH- on the carbonly, loss of -CBr3 (Mechanism B).

4. b-Keto acids and b-dicarboxylic acids can be decarboxylated via a six-membered ring transition state facilitated by a hydrogen bond and six-membered ring conformation that means they are "poised" to react.

Homework: Begin Working on Homework Problem Set 5. It will be due before class next Wednesday, February 27. Reading: Sections 17.4-17.9 Problems in Book: 17.1-17.8, 17.19, 17.22, 17.26, 17.32, 17.35 You will not turn these in but they are very helpful to PREPARE for the next lecture.