Tautomerism in multi-carbonyl compounds Enol

malondialdehyde (propanedial) enolization. example of 1,3-dicarbonyl compound enol stabilized hydrogen bonding, leading detection of percent or less of keto form @ equilibrium.

in organic compounds 2 (or more) carbonyls, enol constitutional isomer may stabilized. in particular, occurs in cases 1,3-dicarbonyl compounds—see examples of 2,4-pentanedione , tartronaldehyde in opening image gallery—that is, when 2 carbonyl groups separated in structure single methylene- or methine-type (-chr-) group [i.e., have structure -c(o)-chr-c(o)-, r=h, alkyl, or other groups]. hence, while 1 α-hydrogen required (see opening image gallery), second substituent in α-position may variable.

enol stabilization due in large part intramolecular hydrogen bonding available it, shown 2,4-pentanedione equilibrium above. in case of malonaldehyde (propanedial), on 99 mole% of compound in enol form. while lower 3-ketoaldehydes , 1,3-diketones, enol form still predominates, e.g., in case of 2,4-pentanedione, 1,3-diketone, 80 mol% in enol form.