Rules of the Day 2-4-08

1. Gilman reagents are very useful because they react as nucleophiles with primary alkyl halides, vinylic alkyl halides (halogen atom attached to sp2 carbon of a double bond) and epoxides at the less hindered site to give new carbon-carbon bonds!

2. The most important feature of carbonyl groups is that the carbon-oxygen double bond is highly polarized, with a partial positive charge on the carbon atom and a partial negative charge on the more electronegative oxygen atom. From this description alone it is clear that nucleophiles will attack the carbon carbon atom (while C=O pi bond breaks) and Lewis acids such as protons will react with the carbonyl oxygen atom. Time capsule: Strong base can remove a hydrogen on carbon atoms adjacent to carbonyl groups to give enolates.

3. There are basically four different mechanisms elements that make up the steps of carbonyl reactions. A) Add a proton, B) Remove a proton, C) Attack with a nucleophile, and D) Departure of a leaving group. These same four mechanism elements describe most of the other mechanisms you have/will learn!!! (Yes, organic chemistry really is this simple if you look at it this way!!)

4. There are basically four different mechanisms that describe the vast majority of carbonyl reactions, which are different combinations/ordering of the four mechanism elements . In this class, I have termed them "Mechanism A", "Mechanism B", "Mechanism C", and "Mechanism D". Click on each to see how they are different. They all involve a nucleophile attacking the partially positively charged carbon atom to create a tetrahedral intermediate. Different reaction mechanisms are distinguished by the timing of protonation of the oxygen atom as well as the presence or absense of a leaving group attached to the carbonyl.

5. Grignard reagents add to aldehydes and ketones to give tetrahedral alkoxide intermediates (can be isolated). These alkoxides are protonated when the chemist opens the flask and adds acid to give alcohols. Mechanism A. Carbon-carbon bond forming!

Homework: Continue working on the third homework problem set, due Wed, 2-6-08, BEFORE CLASS. Click here to download the pdf.

Read: Sections 16.6 Problems: 16.14, 16.15 (You ARE responsible for ketone and aldehyde nomenclature!), 16.18-16.21 in the book You will not turn these in but they are very helpful to PREPARE for the next lecture.