Rules of the Day 2-27-08
Click here for a copy of the mechanism sheet used in lecture today.
Featured Golden Rule of Chemistry: 7. Pi electrons prefer to be delocalized over as many adjacent sp2 hybridized atoms (or sp1 hybridized atoms in some cases) as possible, and aromaticity is the most stable form of pi electron delocalization. Pi electrons cannot delocalize onto or through sp3 hybridized atoms since an sp3 atom has no 2p orbital available.
1. The important carboxylic acid derivatives are acid chlorides, anhydrides, esters, and amides.
2. Amides are interesting functional groups in that the amide nitrogen atom is sp2 hybridized, not sp3 as you might expect. This is because the nitrogen lone pair is delocalized into the carbonyl pi bond. This has very important consequences in that the amide C-N bond does not rotate, and the carbonyl group of amides is less electrophilic than you might think. See the picture of the day for more details.
3. The characteristic reaction mechanism of carboxylic acid derivatives is Mechanism B, with or without a protonation.
4. The key issue with the four main carboxylic acid derivatives is leaving group ability. The better the leaving group ability, the more reactive the carboxylic acid derivative.
5. Listed from most to least reactive with nucleophiles, the carboxylic acid derivatives are acid chlorides, acid anhydrides, esters, amides. This is a big range of activity, as acid chlorides are extremely reactive while amides are extremely unreactive.
Homework: Start Working on Homework Problem Set 6. It will be due before class next Wednesday, March 6. Reading: Sections Problems in Book: 18.14 You will not turn these in but they are very helpful to PREPARE for the next lecture.
