Tautomerization tendencies of 2-acetylcycloalkanones, 2-acetyl-1,3-cycloalkanediones, and cyclic β-keto esters of five- and six-membered rings

Abstract

NMR and kinetics studies of the tautomeric equilibrium of 2-acetylcycloalkanones, 2-acetyl-1,3cycloalkanediones, and methyl 2-oxocycloalkanecarboxylates of five-and six-membered rings have been carried out. By comparing 1 H NMR and 13 C NMR spectra recorded in D 2 O-DOCD 3 and CDCl 3 , with those results derived using a bromination kinetic procedure in dilute aqueous solution, information concerning tautomeric interconversion is provided. Some discussions considering ionisation equilibria and rate constants involved have also been considered. Solvent and concentration effects on keto-enol equilibria have also been discussed.Résumé : On a effectué des études RMN et cinétiques sur l'équilibre tautomère de 2-acétylcycloalcanones, de 2acétylcycloalcane-1,3-diones et de 2-oxocycloalcanecarboxylates de méthyle de composés à cinq et à six chaînons. En comparant les spectres RMN du 1 H et du 13 C enregistrés dans le D 2 O-DOCD 3 et CDCl 3 avec ceux obtenus à l'aide de la méthode cinétique de bromation dans des solutions aqueuses diluées, on en a tiré des informations relatives à l'interconversion tautomérique. On présente aussi quelques discussions relatives à l'équilibre d'ionisation et aux constantes de vitesse. On discute aussi des effets de solvant et de concentration sur l'équilibre cétoénolique.

The quest for odorants having salicylate notes

“…Calculations using the standard Monte Carlo procedure show that the best conformer for the 2‐propionylcyclohexanone is, as expected, the enol form. Later, this was fully confirmed by the NMR spectra of the compounds obtained . Such compounds are readily accessible via condensation of an enamine with an acid chloride (Scheme ).…”

“…Later, this was fully confirmed by the NMR spectra of the compounds obtained. [35][36][37] Such compounds are readily accessible via condensation of an enamine with an acid chloride [38][39][40][41][42][43][44] (Scheme 5). The olfactory evaluations of these β-keto esters and β-diketones are summarized in Table 3.…”

Determination of the enol form of asymmetric 1,3-dicarbonyl compounds: 2D HMBC NMR data and DFT calculations

“…Compounds 1-10 were isolated by column chromatography and characterized by 1 H-, 13 C-NMR, and FT-IR spectroscopies. In CDCl 3 solution, all molecules 1-10 were in the enol form, which was manifested by the signal of the R 1(2) C(=O)CH=C(OH)R 2(1) (6-6.5 ppm) enol form in the NMR spectra.…”

“…It is well known that the keto-enol tautomerization depends on polarity of solvent and this could be explained in terms of the solvation of the carbonyl groups by the molecules of a polar solvent, thus increasing the relative stability of the keto form. 13 Moreover, the formation of an intramolecular hydrogen bond leads to the enol form having a pseudo-cyclic system in its structure, which is more favourable in non-polar solvents. The cis-enol forms of 1,3-dicarbonyl compounds are stabilized by a strong intramolecular hydrogen bond.…”

β-cetoamidas: estudio de equilibrios tautoméricos y reactividad química

“… Utilización de compuestos modelo de los cuales se conozca con certeza que existan exclusivamente en una de las dos formas tautoméricas. Se han encontrado efectos de la concentración 141,142 y de la temperatura [143][144][145][146] que llevaron a determinar valores de H 0 y de G 0 .…”