nonenolizable

Nonenolizable is a term used in organic chemistry to describe carbonyl-containing compounds that cannot form an enolate ion or enol tautomer because there are no hydrogen atoms on the alpha carbon, the carbon adjacent to the carbonyl group. Enolization requires an alpha hydrogen; when none are available, enolate chemistry such as aldol reactions, Michael additions, or enolate alkylations is not available under ordinary conditions.

This situation arises when the alpha positions are substituted with hydrogen-free groups, typically because the carbon next to the carbonyl is part of an aryl ring or is otherwise quaternary. Common examples include benzaldehyde (Ph-CHO) and benzophenone (Ph-CO-Ph). In these cases there are no alpha hydrogens on the side(s) of the carbonyl, so enolization is effectively precluded.

In practical terms, nonenolizable carbonyls influence synthetic planning by excluding them from routes that rely on enolate chemistry. Reactions with these compounds proceed via non-enolate pathways, such as direct nucleophilic additions to the carbonyl, acyl substitutions, or electrophilic aromatic substitutions on attached aryl rings.

Notes: whether a carbonyl compound is nonenolizable can depend on the reaction conditions; very strong bases or unusual catalysts might promote rare enolization in some cases. However, under standard conditions, these compounds are considered unable to form enolates due to lack of alpha hydrogens.