Thermodynamic Enolates
Thermodynamic Enolates - Related Videos
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Third Law of Thermodynamics
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2020
A pure, perfectly crystalline solid possessing no kinetic energy (that is, at a temperature of absolute zero, 0 K) may be described by a single microstate, as its purity, perfect crystallinity,and complete lack of motion means there is but one possible location for each identical atom or molecule comprising the crystal (W = 1). According to the Boltzmann equation, the entropy of this system is zero. This limiting condition for a system’s entropy represents the third law of thermodynamics: the...
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Second Law of Thermodynamics
0 Views •
2020
In the quest to identify a property that may reliably predict the spontaneity of a process, a promising candidate has been identified: entropy. Processes that involve an increase in entropy of the system (ΔS > 0) are very often spontaneous; however, examples to the contrary are plentiful. By expanding consideration of entropy changes to include the surroundings, a significant conclusion regarding the relation between this property and spontaneity may be reached. In thermodynamic models, the...
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Second Law of Thermodynamics
0 Views •
2019
The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. Each energy transfer results in a certain amount of energy that is lost—usually in the form of heat—that increases the disorder of the surroundings. This can also be demonstrated in a classic food web. Herbivores harvest chemical energy from plants and release heat and carbon dioxide into the environment. Carnivores harvest the chemical energy...
01:19
Types of Enols and Enolates
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2025
Aldehydes and ketones form enols, although only about 1% of the enol is present at the equilibrium for simple monocarbonyl compounds. The enol form is undetectable for acetaldehyde, present as only 1.5 × 10−4 % of acetone, and present as only 1.2% of cyclohexanone. Two kinds of regioisomeric enols are possible for unsymmetrical ketones, and their net composition is 1% at equilibrium. This instability is due to the lower bond energy of C=C than the C=O group. The additional instability of enols...
00:37
First Law of Thermodynamics
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2019
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed. This can be demonstrated within a classic food web where light energy from the sun is harnessed as radiant energy by plants, converted into chemical energy, and stored as complex carbohydrates. The vegetation is then consumed by animals and during the digestion process, the sugars release energy as heat. The sugars also produce chemical energy that either gets used up doing work, stored in...
FAQs
Equilibration allows each enolate to undergo reprotonation and subsequent deprotonation, so the initially formed species can convert into alternatives. Repeated interconversion gradually shifts the mixture toward the enolate with greater thermodynamic stability rather than preserving the first product generated. This process explains why reaction time and reversible conditions influence the observed regioselectivity.
A more substituted alkene is often associated with greater enolate stability, so equilibration can increase its proportion relative to a less substituted alternative. The preference reflects the relative stability of the competing species, not necessarily the speed of their initial formation. Consequently, thermodynamic control commonly gives the regioisomer corresponding to the more substituted alkene.
Kinetic enolates reflect the fastest deprotonation pathway and are favored by low temperature and steric control. Thermodynamic enolates emerge when reversible deprotonation permits interconversion, typically with a strong base, higher temperature, or longer reaction time. The two approaches can therefore produce different regioisomers because one emphasizes formation rate while the other emphasizes relative stability.
Conditions that permit equilibration favor thermodynamic enolates. The overview identifies a strong base, elevated temperature, and extended reaction time as important factors because they support repeated deprotonation and reprotonation. In contrast, low-temperature, sterically controlled conditions favor kinetic selection. Adjusting these variables changes which competing enolate predominates before the subsequent synthetic transformation.
A chemist first identifies the competing carbonyl-derived enolates, then selects conditions that allow them to interconvert rather than trapping only the fastest-formed species. A strong base, increased temperature, or longer reaction time can promote equilibration. The resulting distribution is evaluated through relative enolate stability, allowing selection of the regioisomer expected to support the desired transformation.
Thermodynamic enolate control helps predict which carbon atom of a carbonyl compound will participate in carbon-carbon bond formation. In aldol reactions, alkylations, and related transformations, favoring the more stable enolate can direct formation toward a particular regioisomer. This makes equilibration conditions useful when synthetic planning requires control over connectivity rather than simply the fastest reaction pathway.