Rules of the Day
3-28-2024
Click here for a copy of the lectures notes I wrote in class
Click here for a copy of the first handouts I used in class today
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.
1. Synthesis with enolates formed from LDA changes everything! LDA is such a strong base that it allows you to make entire samples of aldehyde, ketone and ester enolates. These can be used in 1) "crossed" or "mixed" reactions 2) Michael reactions 3) alkylations with haloalkanes (SN2) or 4) acylations with acid chlorides (Mechanism B). Reactions 2) - 4) make them analogous to enamines.
2. When thinking about LDA and equivalents, you need to understand each mechanism and THE MINIMUM AMOUNT OF BASE NEEDED TO COMPLETE EACH REACTION (catalytic HO- for aldol, 0.5 equivalents for Claisen, etc.). Remember, by definition, the organic starting material is present as 1.0 equivalent. The key difference is that LDA quantitatively makes enolates from aldehydes, ketones and esters, while weaker bases only make a small amount. Keep track of much of the starting organic piece (aldehyde, ketones, esters) left over after base is added.
3. You need to know all the enolate reactions and how to use them. The best way to learn these is by putting them on a roadmap. You also need to learn the KRE's of the different enolate reactions, keeping in mind that several are hard to spot. It takes practice!! That is the only way to solve synthesis problems. Remember to work backwards and count carbons.
4. I believe that Organic chemistry involves all levels of higher order thinking described in the Bloom's Taxonomy of learning pyramid. Click here to see a Pictures of the Day that describes this in detail, with links to the various "tools" we have created to help you succeed in masteing all of the levels of the pyramid.
If you are having trouble understanding carbonyl mechanisms or the concepts surrounding the equivalents of base used in enolate reactions you should look at the handouts by clicking on those links.
I have made a number of short videos to helps explain topics that many students find confusing. You should watch these if you are having trouble with any of the following subjects:
Beta-dicarbonyl enolate sterics
Balancing an equation for the Claisen reaction
What is up with -OH, -OEt and LDA in enolate reactions? (mistake on the last page edition)! Click here to see the corrected version of the -OH, -OEt and LDA in enolate reaction video
5. H-X and X2 add to conjugated dienes to give both 1,2 and 1,4 addition products, via a resonance stabilized allylic cation intermediate.
6. The 1,2 addition is usually the kinetic product, that is, it forms faster (better opportunity since the reaction is occuring at a more stabilized secondary carbocation), but the 1,4 addition product is the thermodynamic product because it is more stable (greater motive since the double bond is more substituted). At low temperature, in which the molecules cannot equilibrate, the kinetic product predominates (called kinetic control). At higher temperature, in which the products do equilibrate with each other, the thermodynamic product predominates (called thermodynamic control).
Homework:
Read: Sections 20.1 - 20.3 in the ebook textbook. This text is part of the Longhorn Textbook access program.
Take the Daily Quiz 16 before 10 PM tomorrow. Click here to access the quiz.
Finish working on the Homework Problem Set 8, due at 10 PM on Monday, April 1. Click here to access the Homework Problem Set 8. This IS AN IMPORTANT ONE!! We will be grade it for completion only. There is no Aktiv learning portion of this homework, just Gradescope.