¹H and ¹³C NMR study of the enol–enolic tautomerism of some cyclic β‐ketoaldehydes

Abstract

Abstract Aldehyde (δCH) and enolic (δOH) proton chemical shifts, the corresponding spin–spin coupling constants ( J CH,OH) and the 13 C chemical shifts (δC) have been measured for three cyclic β‐ketoaldehydes as a function of temperature. A tautomeric equilibrium has been shown to exist between the aldo–enol ( A ) and hydroxymethylene ketone ( B ) forms. The chemical shifts δCH δOH and δC for the two pure tautomeric forms A and B have been calculated. The enthalpy changes Δ H in the tautomeric process A ⇄ B and the percentages of the tautomeric forms have been determined.