ABSTRACT
Keto-enol tautomerism was discussed in Section 10.7 in connection with the hydration reaction of alkynes, as well as oxymercuration or hydroboration. A ketone or an aldehyde exists with small amounts of the enol form in most cases. e carbonyl form is more stable, and for most aldehydes and ketones, only a tiny amount of enol is present. As shown by the equilibrium arrows in Figure 22.1, acetone (propan-2-one) exists primarily as the ketone, and while some enol (prop-1-en-2-ol) is present, experiments show the presence of only 1.5 × 10-4% enol.1 e proton of an enol is acidic, as indicated by the δ+ dipole in Figure 22.1, but the α proton on the α carbon is also acidic. e α proton is polarized due to the inductive eects of the proximal carbonyl unit, leading to the δ+ dipole on the α-proton. erefore, a ketone and aldehydes are considered to be weak acids.
