The carbon next to the carbonyl group is designated as being in the alpha position. Electrophilic substitution occurs at this position through either an enol or an enolate: ketos and enols act as nucleophiles, so they react with electrophiles, ketos and enols are constitutional isomers, not anything else (ex. Structures or any other type of isomers): difference in bonding pattern, differ on how the atoms are connected. Keto and enol form are in equilibrium with each other. Keq for keto-enol equilibrium can vary widely. (1,3-dicarbonyl compounds): when the enol form is particularly stabilized by conjugation, the enol form dominates. In this case, the keto form is formed between 10% to 30% and the enol form is formed between. The enol form of the first is more stable than the keto form because of conjugation. You might think the enol form in the third pair has (cid:272)o(cid:374)jugatio(cid:374) a(cid:374)d it does. But aro(cid:373)ati(cid:272) (cid:272)o(cid:374)jugatio(cid:374) is(cid:374)"t as sta(cid:271)le, so it does(cid:374)"t (cid:272)ou(cid:374)t.
