Enolates charge distribution

Examine the enolate of acetone on Learn mg By Modeling How IS the negative charge distributed between oxygen and the a carbon" ... 

Which of the two enolates enolate A or enolate B) is lower in energy Rationalize your observation by comparing their structures, charge distributions and electrostatic potential maps. Draw all of the resonance contributors needed to describe each enolate. Which enolate is generated by reaction with NaH ... 

Crown or solvent complexation leading to loose ion pairs can by itself cause a drastic change in the charge distribution of the anion. A good example is found in reaction 4 studied by Boche et al (19). At room temperature the sodium enolate tight ion pair with... 

The very important reactive intermediate, the enolate ion, is an example of a Z-substituted carbanion. The charge distribution and HOMO obtained by SHMO calculation are shown below ... 

RB3LYP calculations indicate that the s-cis conformer of peroxy acids is more stable than the s-trans conformer. Calculations on the reaction of prop-2-enol with some peroxy acids showed that trans-transition states collapse to the epoxide via a 1,2-shift, whereas a 1,4-shift is operable for cis-transition states.195 Quantum mechanical calculations have been performed on the migration step of the Baeyer-Villiger rearrangements of some substituted acetophenones with m-chloroperbenzoic acid (m-CPBA). The energy barriers, charge distributions and frontier molecular orbitals, determined for the aryl migration step, have been used to explain the effects of substituents on the reactivity of the ketones.196... 

Ambident anions are mesomeric, nucleophilic anions which have at least two reactive centers with a substantial fraction of the negative charge distributed over these cen-ters ) ). Such ambident anions are capable of forming two types of products in nucleophilic substitution reactions with electrophilic reactants . Examples of this kind of anion are the enolates of 1,3-dicarbonyl compounds, phenolate, cyanide, thiocyanide, and nitrite ions, the anions of nitro compounds, oximes, amides, the anions of heterocyclic aromatic compounds e.g. pyrrole, hydroxypyridines, hydroxypyrimidines) and others cf. Fig. 5-17. 

Fig. 3.37. Differential reaction energy profiles for O versus C alkylation of enolates. (a) O-Alkylation is characterized by an early transition state, weak O-solvation, high anion reactivity, and relatively large electrostatic effects, (b) C-Alkylation is characterized by a later transition state with more C—C bond formation and more diffuse charge distribution.

The kinetics and mechanism of the acid-catalysed reactions of methylated trioses have been determined and the results were shown to be in good agreement with quantum mechanical calculations of charge distributions in substrates and intermediates. The same group has studied the kinetics and mechanism of acid-base-catalysed enolization of glycolaldehyde and methoxyacetaldehyde by polarography. Deuterium incorporation was used to establish the mechanism. ... 

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