Determination of Solvent Effects on Keto—Enol Equilibria of 1,3-Dicarbonyl Compounds Using NMR

Cook, A. Gilbert; Feltman, Paul M.

doi:10.1021/ed084p1827

Cited by 44 publications

(40 citation statements)

References 11 publications

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“…11,24,77,78 Acyclic β-diketones and β-ketoesters follow Meyer’s rule of a shift in the tautomeric equilibrium toward the keto tautomer with increasing solvent polarity because the keto form is more polar than the enol form and hence is more stable in polar solvents. 78 However, a report on keto–enol tautomerization of some specific Schiff bases demonstrated an opposite solvent-dependent effect. 79 We have extended our computational effort to examine the impact of solvent polarity on the keto–enol tautomerization process of the cyclic diketo systems using the SMD solvation model with acetonitrile (35.7) at M062X-SMD acetonitrile /6-31+G(d,p)//M062X/6-31+G(d,p) and n -hexane (1.9) at M062X-SMD hexane /6-31+G(d,p)//M062X/6-31+G(d,p).…”

Section: Resultsmentioning

confidence: 99%

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DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto–Enol Tautomerization Process of α- and β-Cyclodiones

Jana

Ganguly

2018

ACS Omega

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We have explored the effect of ring size on keto–enol tautomerization of α- and β-cyclodiones using the M062X-SMD aq /6-31+G(d,p)//M062X/6-31+G(d,p) level of theory. The calculated results show that the activation free energy barrier for the keto–enol tautomerization process of α-cyclopropanedione ( 1 ) is 54.9 kcal/mol, which is lower compared to that of the other cyclic diketo systems studied here. The four-membered α- and β-cyclobutanedione ( 2 and 6 ) do not favor keto–enol tautomerization unlike other studied cyclic systems because of the ring strain developed in the transition-state geometries and their corresponding products. Water-assisted keto–enol tautomerization with one molecule reveals that the free energy activation barriers reduce almost half compared to those for the uncatalyzed systems. The two-water-assisted process is favorable as the activation free energy barriers lowered by ∼10 kcal/mol compared to those of the one-water-assisted process. The ion-pair formation seems to govern the lowering of activation barriers of α- and β-cyclodiones with two water molecules during the keto–enol tautomerization process, which however also overcomes the favorable aromatization in the three-membered ring system. The free energy activation barriers calculated with the M062X-SMD aq /6-31+G(d,p) level predicted that the keto–enol tautomerization process for the α-cyclodiones follows the following trend: 2 > 3 > 4 > 5 > 1 . Water-assisted tautomerization of α-cyclodiones also predicted 1-W and 1-2W as the most favored processes; however, 5-W and 5-2W were found to be disfavored in this case. The β-cyclodione systems also showed similar trends as obtained with α-diketone systems. The influence of bulk solvent on the keto–enol tautomerization process favors the formation of the enol form in a more polar solvent medium even under mixed solvent conditions in acetonitrile and hexane at M062X-SMD acetonitrile /6-31+G(d,p) and M062X-SMD hexane /6-31+G(d,p) levels of theory.

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Section: Resultsmentioning

confidence: 99%

“…These results suggest that the keto–enol tautomeric equilibrium can be altered with cyclic diketones compared with the acyclic systems using different solvent media. 24,78…”

Section: Resultsmentioning

confidence: 99%

DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto–Enol Tautomerization Process of α- and β-Cyclodiones

Jana

Ganguly

2018

ACS Omega

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“…It was confirmed by 1 H NMR spectra: a broad signal of the OH group (around 14.9–15.3 ppm) along with a sharp signal of protons attached to the C=C enol bond (around 6.5 ppm) were observed in all spectra. Conversely, no signals of the CH 2 moiety were observed [36]. As one might have expected, a solution of 1-(2-thienyl)butane-1,3-dione ( 5 ) in CDCl 3 contains both forms, keto ( 5 ) and enol ( 7 ), in a molar ratio of 1:5 (Scheme 4).…”

Section: Resultsmentioning

confidence: 97%

A convenient and practical synthesis of β-diketones bearing linear perfluorinated alkyl groups and a 2-thienyl moiety

Taydakov¹,

Kreshchenova²,

Dolotova³

2018

Beilstein J. Org. Chem.

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A versatile and robust synthetic protocol for the preparation of β-diketones bearing 2-thienyl and perfluorinated alkyl radicals of different length or a methyl group was developed. This protocol is suitable for the preparation of multigram quantities of diketones without cumbersome purification procedures. Moreover, the known method for purification of diketones via copper chelates was improved considerably.

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“…The analysis of 1 H NMR spectra of the β-dicarbonyl derivatives 3a–i in CDCl 3 revealed that a keto–enol tautomerism exists only for the acetylacetone derivative 3g and its enolic form 5g in a 54:46 ratio, respectively (Table 2, entry 7), whereas the other compounds 3a–f , 3h and 3i are exclusively in the β-dicarbonyl form [45–47]. …”

Section: Resultsmentioning

confidence: 99%

Et₃B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

Abidi¹,

Oueslati²,

Rezgui³

2016

Beilstein J. Org. Chem.

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Determination of Solvent Effects on Keto—Enol Equilibria of 1,3-Dicarbonyl Compounds Using NMR

Cited by 44 publications

References 11 publications

DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto–Enol Tautomerization Process of α- and β-Cyclodiones

DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto–Enol Tautomerization Process of α- and β-Cyclodiones

A convenient and practical synthesis of β-diketones bearing linear perfluorinated alkyl groups and a 2-thienyl moiety

Et₃B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

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Determination of Solvent Effects on Keto—Enol Equilibria of 1,3-Dicarbonyl Compounds Using NMR

Cited by 44 publications

References 11 publications

DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto–Enol Tautomerization Process of α- and β-Cyclodiones

DFT Study To Explore the Importance of Ring Size and Effect of Solvents on the Keto–Enol Tautomerization Process of α- and β-Cyclodiones

A convenient and practical synthesis of β-diketones bearing linear perfluorinated alkyl groups and a 2-thienyl moiety

Et3B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols

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Et₃B-mediated and palladium-catalyzed direct allylation of β-dicarbonyl compounds with Morita–Baylis–Hillman alcohols