Click here for a copy of the mechanism sheet used in lecture today.
A. Tips for test preparation; what you need to know
Know the mechanisms, and understand how each step makes sense. BE ABLE TO IDENTIFY EACH STEP IN EACH MECHANISM AS ONE OF THE FOUR MECHANISTIC ELEMENTS (add a proton, take away a proton, attack with a nucleophile and lose a leaving group).
Know all the KRE's (Key Recognition Elements) for the different reactions, concentrating on the C-C bond-forming reactions
Know how to use the pKa table!
Be able to use all the reactions in the roadmap you have made
B. Tips for test preparation; what you should do to prepare
By yourself:
Master the reactions, mechanisms, KRE's, and analyze the homework and old exam answers. KNOW YOUR STUFF!
Make a sheet that lists the PRODUCTS of all the reactions first, then fill in the starting materials
With study partners:
Make up problems for each other in which you derive a product of a reaction. Show your study partner the products, and have them deduce the starting materials and reagents.
Make up synthesis problems for each other, by running a series of reactions on a randomly chosen starting material. Show your study partners the final product and the starting material, and have them fill in the rest.
Rules of the Day 3-24-08
1. There are four new concepts associated with chapter 19. Click on these one at a time to get more information.
C) Beta-Dicarbonyl species are especially acidic
D) Conjugate addition to alpha,beta unsaturated carbonyl species.
2. Aldols between two different aldehydes can be run in high yield if one of the carbonyls is a ketone and the other is an aldehyde that cannot make an enolate. This is generally only relevant to formaldehyde and benzaldehyde.
3. A Claisen reaction is an "aldol with esters", also known as Dr. Evil meets an ester. At least 0.5 equivalents of the alkoxide corresponding to the alcohol portion of the ester is used to create an enolate that reacts with another molecule of ester via Mechanism B. For a movie of the Claisen reaction, click here. Claisen reactions are favorable (have a strong motive) because of the last deprotonation step.
4. The amount of base you add matters!! Only a catalytic amount of hydroxide is needed for an aldol to work, but at least 0.5 equivalents of alkoxide are needed for a Claisen to go to completion.
5. WARNING Cyclic aldol and Claisen reactions (called a Dieckmann reaction) can be hard to figure out. They work best when forming 5 or 6 membered rings and the best thing for you to do is to number your carbon atoms.
Homework: Begin studying for next week's midterm! Read: No new reading Problems: No new problems
