Investigation of Keto–Enol Tautomerism by Nuclear Magnetic Resonance Spectroscopy

Kinetics of monochelation of aqueous chromium(III) by methyl 2-oxocyclopentanecarboxylate

“…The failure of malonic ester to enolize 9 and the increasing degree of enolization with increasing electron-accepting capacity of the substituents are consistent with this view. 38,39 It is interesting that the extent of the enol contribution to the structure of HMCP is less than that of any other of the alkyl 2-oxocycloalkanecarboxylates mentioned, which is presumably related to the low electron-accepting capacity of the substituent.…”

“…Conversely, polar solvents displace the equilibrium towards the polar diketo form. 9 This can be explained by the solvation of the carbonyl groups by the polar solvent molecules, which increases the stability of the keto forms, and this is found to be true in the case of methyl 2-oxocyclopentanecarboxylate. In fact, our analysis of the 1 H and 13 C NMR spectra indicated that the keto tautomer of methyl 2-oxocyclopentanecarboxylate (HMCP k ) was present in D 2 O-CD 3 OD aqueous solution at 25°C, while the enol tautomer (HMCP e ) was undetected, indicating less than 5% of enol form in the medium.…”

“…1 Alkyl esters of 2-oxocycloalkanecarboxylic acids are receiving considerable attention, not only from the viewpoints of synthesis,2-5 reactivity [6][7][8] and spectroscopic behaviour, 9 but also because of their pharmacological and therapeutic properties, which make them useful lead compounds for the development of safer antiepileptic drugs 10 or derivatives with anti-inflammatory effects. 11 Furthermore, they exhibit the phenomenon of ketoenol tautomerism and are able to form complex compounds similar to those of b-diketones.…”

Tautomerism: Introduction, History, and Recent Developments in Experimental and Theoretical Methods

“…In 1931, Raman effect was discussed in relation to the tautomerism of acetoacetic ester by Dadieu and Kohlrausch [54]. According to Kol'tsov and Kheifets [55], the first study in which NMR was employed to investigate tautomerism was published in 1953 [56]. Although mass spectrometry is not related to solution, we have to recognize the first attempts (in 1967) devoted to its application in the structural study of tautomeric compounds [57].…”

Theoretical studies of the equilibria between two enolic forms of asymmetric ?-diketones

“…1 -4 In particular, the equilibria in keto-enol tautomerizations ofˇ-diketones have been extensively studied. 3,4 Since the rate of keto-enol conversion of aˇ-diketone is generally slow, the NMR signals of two tautomers can be separated to determine their relative ratio by intensity measurements. The cis-enolic form of aˇ-diketones has also received much attention because of the presence of the intramolecular hydrogen bonding and the rapid hydrogen tautomerization.…”