Enolates Flashcards
What is the following reaction:
This is acid catalyzed tautomerization. The first step is missing here- the first step is the protonation of the carbonyl oxygen that makes the positive charge on the molecule.
What is the following reaction:
Base catalyzed tautomerization.
Which of the following is thermodynaically favorable and which is kinetically favorable:
The product shown furthest to the right is the kinetically favored product (less stable, forms in low temp) and the one to the left is the thermodynamically favored one (high temps and more stable)
Would the following occur under acidic or basic conditions?
Basic
When will the enol form predominate instead of the keto form?
This is an example of a molecule in which the enol form would predominate over the keto form due to extended conjugation, in particular with aromaticity. As shown below, the enol form has a benzene ring, which is cyclic and conjugated, and has 4n +2 = 6 pi electrons and is therefore aromatic. The keto form is not completely conjugated and therefore not aromatic.
What enolate will form?
This is the kinetic enolate, which is formed by removing a proton from the less substituted alpha carbon, so it is less stable; however, the kinetic enolate is formed more rapidly because the alpha proton is less sterically hindered. Therefore, the kinetic enolate is favored by irreversible conditions like lower temperature and a very strong, bulky base like LDA.
WHat enolate will form:
This is the thermodynamic enolate, formed at the more substituted alpha carbon, so it is more stable. However, it forms more slowly than the kinetic enolate because the more substituted carbon is more sterically hindered, so it is favored by a smaller base like hydroxide and reversible conditions such as (1) room temperature or higher and (2) a (relatively) weaker base like hydroxide or an alkoxide. Formation of the thermodynamic enolate is highlighted in the box below.
True or False: REversible reactions favor the kinetic product
False.
What is LDA?
LDA is lithium diisopropylamide. It is a strong bulky base. Used in aldol condensations.
Why is LDA used with low tempurature conditions in the first part of the reaction?
This whole reaction described an aldol condensation. Using LDA in low temps assures us that the base will deprotonate at the less substituted carbon because low temps favor the KINETIC products.
Whys is water used at the end of this reaction?
This is the condensation step of the reaction! Without it, youd just get an aldol
What is the following structure?
Enolate
What kind of base is ammonia?
Weak
