Enolization enolizable hydrogen atom

If an asymmetric carbon atom has an enolizable hydrogen atom, a trace of acid or base allows that carbon to invert its configuration, with the enol serving as the intermediate. A racemic mixture (or an equilibrium mixture of diastereomers) is the result. 

Only a-hydrogen atoms are exchanged because the reaction occurs through an enolate ion intermediate. All possible enolizable hydrogen atoms are eventually replaced. The hydrogen atoms are lost in the solvent, which contains many more deuterium atoms than the number of hydrogen atoms transferred from the carbonyl compound. 

In addition to its mechanistic importance, keto-enol tautomerism affects the stereochemistry of ketones and aldehydes. A hydrogen atom on an a carbon may be lost and regained through keto-enol tautomerism such a hydrogen is said to be enolizable. 

Sometimes a Lewis acid such as zinc iodide is added in catalytic amounts. Side reactions may sometimes occur if acyl cyanides carry hydrogen atoms in the a-position and are, therefore, enolizable. In those examples trimethylsilyl chloride, which is formed during the reaction, may react to give trimethyl-silylated enol ethers (8). This methodology can be applied successfully to the synthesis of such com-... 

Surfaces with basic sites form enolates from both the aldehydes and ketones, leading to multiple aldol condensations and Michael additions. " Candidate molecules must be enolizable, i.e., contain an a-hydrogen atom. Aldol condensation / Michael addition products cover the range from a,p-unsaturated aldehydes, saturated aldehydes, hydrogenated products (alcohols), and the heavier aromatics resulting from multiple condensations. The presence of coordina-... 

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