Thermodynamic Enolates
Thermodynamic Enolates - Related Videos
02:38
Third Law of Thermodynamics
0 Views •
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...
02:49
Second Law of Thermodynamics
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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...
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...
01:18
Reactivity of Enols
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2023
Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A carbonyl compound with an α hydrogen undergoes keto–enol tautomerism and remains in equilibrium with its tautomer, the enol form. Usually, the keto tautomer is present in a higher concentration than the enol tautomer due to the higher bond energy of C=O compared to C=C. Moreover, the direction of the keto–enol equilibrium is governed by factors like...
02:16
First Law of Thermodynamics
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2020
Energy Conservation Energy can be converted from one form into another, but all of the energy present before a change occurs always exists in some form after the change is completed. This observation is expressed in the law of conservation of energy: during a chemical or physical change, energy can be neither created nor destroyed, although it can be changed in form. According to the law of conservation of matter, there is no detectable change in the total amount of matter during a chemical...
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.