Tautomeric equilibrium of 2-hydroxypyridine/2-pyridone: does a theoretical—experimental discrepancy exist?

Parchment, Oswald G.; Burton, Neil A.; Hiller, Ian H.

doi:10.1016/0009-2614(93)89308-5

Cited by 37 publications

(14 citation statements)

References 17 publications

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“…This result agrees with the experimental values recorded by other workers [19,20]. It also agrees with the theoretical calculations [33,34,40]. This ∆G has been taken as reference for determining the relative stability of Xsubstituted 2-pyridone and 2hydroxypyridine.…”

Section: -Pyridone (A) 2-hydroxypyridine (B) Schemesupporting

confidence: 92%

“…The calculated Gibbs free energy (∆G) for the tautomerization (Scheme 3) is 7.140 kcal/mol, suggesting that 2-pyridone was predominant. This agrees with theoretical and experimental predictions [33,34,40]. This ∆G was taken as a reference for determining the relative stability of X-substituted 2-pyridone and 2-hydroxypyridine.…”

Section: A) Parent Compounds (2-pyridone and 2hydoxypyridine)supporting

confidence: 85%

“…The calculations were first performed on a parent compounds (2-pyridone and 2-hydroxypyridine without substitution), and then on a substituted parent compounds. [32,34,49].…”

Section: Am1 Calculations In the Gas Phase (ε =1)mentioning

confidence: 99%

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Tautomeric Equilibria of Substituted 2-Pyridone/2-Hydroxypyridine in the Gas and Aqueous Phases

Alhatem

2018

CSIJ

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Heats of formation, entropies and Gibbs free energies for the twenty structures of substituted 2pyridone and 2-hydroxypyridine were studied using semiempirical Austin Model (AM1) and Parametric Method 3 (PM3) calculations at the self-consistent field level, both in the gas and liquid phases, with full geometry optimization. It was revealed from the study that 2-hydroxypyridine is predominant in gas phase, while 2-pyridone in the liquid phase which agrees with the experimental and theoretical predictions. All substituents such as F, Cl, OH, CH 3 , NH 2 , NO 2 , CHO, CN, CF 3 stabilize the 2-pyridone in the gas and liquid phases except F, Cl and NH 2 in PM3 calculations in the gas phase. The substituents stabilization is more effective in liquid phase. This was also confirmed by thermodynamic calculations and isodesmic reactions.

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Section: -Pyridone (A) 2-hydroxypyridine (B) Schemesupporting

confidence: 92%

Section: A) Parent Compounds (2-pyridone and 2hydoxypyridine)supporting

confidence: 85%

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Tautomeric Equilibria of Substituted 2-Pyridone/2-Hydroxypyridine in the Gas and Aqueous Phases

Alhatem

2018

CSIJ

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“…4,5 While the ground-state tautomers (T) of ESIPT systems are often reasonably assumed to be unstable (i.e., with no ground-state local minimum at the equilibrium nuclear configuration of the excited-state T*), nevertheless a few stable ground-state tautomers of ESIPT systems have been observed or inferred. [6][7][8][9][10][11][12][13][14] It is evident that the polarity and H-bonding strength of solvents affect the stabilization of ground-state tautomers. Recently 15,16 Bisht et al interpreted the pressureinduced increase of the emission intensity of salicylic acid in nonpolar methylcyclohexane as partly due to increased formation of the ground-state tautomer with pressure.…”

Section: Introductionmentioning

confidence: 99%

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

et al. 1999

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Solutions of sodium salicylate in anhydrous polar solvents exhibit a weak, temperature-dependent absorption band (λ max ≈ 325 nm) lying in the Stokes gap between the main absorption (296 nm) and the fluorescence band (396 nm, acetonitrile). This weak, longer wavelength absorption band is hardly observable in aqueous solution, but its intensity increases with temperature and increases with polarity in anhydrous organic solvents in the order of ethanol < acetonitrile < dimethyl sulfoxide at room temperature. After correction for solvent thermal contraction, the temperature-dependent absorption spectrum of salicylate in acetonitrile solutions reveals a clear isosbestic point ( 310 ) 2000 M -1 cm -1 ) characteristic of an equilibrium between two salicylate species with band-maximum extinction coefficients of 325 ) 3400 M -1 cm -1 and 296 ) 3586 M -1 cm -1 . In acetonitrile at room temperature (298 K) the concentration equilibrium constant (minor/major) for the interconversion reaction between the two species is K 298 ) 0.11, with ∆H ) 1.6 kcal mol -1 and ∆S ) 0.97 cal‚mol -1 K -1 . The fluorescence lifetime (4.8 ns in acetonitrile) and the shape of the fluorescence spectrum are independent of excitation wavelength. The fluorescence quantum yield for excitation in the long-wavelength shoulder (340 nm) is approximately 60% larger than the yield for excitation in the main band at 296 nm ( 340 ) 0.29, 296 ) 0.18) in acetonitrile at room temperature. These results are consistent with assignment of the shoulder band to the proton-transfer tautomer of the salicylate anion. Electronic structure calculations support assignment of the 325 nm absorption band to the ground-state tautomer (phenoxide anion form) of the salicylate anion. Absorption transition moments for both the normal and tautomer forms are parallel to the emission transition moment, are electronically allowed, and are consistent with 1 L b assignment for both absorbing and emitting transitions. The static dipole moments are in the order of µ(N*) g µ(N) > µ(T*) > µ(T) for the normal (N) and tautomer (T) ground and electronic excited states.

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“…It tautomerizes to form 2-pyridone (2-PY) by a proton transfer between the nitrogen and oxygen atoms [1]. The tautomerism between 2-hydroxypyridine and 2-pyridone has been confirmed by X-ray [2], IR [3,4,5], UV [6], and microwave spectroscopy [7], together with some theoretical studies [8,9,10]. 2-Pyridones play important roles in bioactive systems and in current medicinal chemistry.…”

Section: Introductionmentioning

confidence: 99%

The Thermodynamic and Kinetic Properties of 2-Hydroxypyridine/2-Pyridone Tautomerization: A Theoretical and Computational Revisit

Hejazi

Osman

Al‐Youbi

et al. 2016

IJMS

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The gas-phase thermal tautomerization reaction between 2-hydroxypyridine (2-HPY) and 2-pyridone (2-PY) was investigated by applying 6-311++G** and aug-cc-pvdz basis sets incorporated into some density functional theory (DFT) and coupled cluster with singles and doubles (CCSD) methods. The geometrical structures, dipole moments, HOMO-LUMO energy gaps, total hyperpolarizability, kinetics and thermodynamics functions were monitored against the effects of the corrections imposed on these functionals. The small experimental energy difference between the two tautomers of 3.23 kJ/mol; was a real test of the accuracy of the applied levels of theory. M062X and CCSD methods predicted the preference of 2-HPY over 2-PY by 5–9 kJ/mol; while B3LYP functional favoured 2-PY by 1–3 kJ/mol. The CAM-B3LYP and ωB97XD functionals yielded mixed results depending on the basis set used. The source of preference of 2-HPY is the minimal steric hindrance and electrostatic repulsion that subdued the huge hyperconjugation in 2-PY. A 1,3-proton shift intramolecular gas-phase tautomerization yielded a high average activation of 137.152 kJ/mol; while the intermolecular mixed dimer interconversion gave an average barrier height of 30.844 kJ/mol. These findings are boosted by a natural bond orbital (NBO) technique. The low total hyperpolarizabilities of both tautomers mark out their poor nonlinear optical (NLO) behaviour. The enhancement of the total hyperpolarizability of 2-HPY over that of 2-PY is interpreted by the bond length alternation.

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Tautomeric equilibrium of 2-hydroxypyridine/2-pyridone: does a theoretical—experimental discrepancy exist?

Cited by 37 publications

References 17 publications

Tautomeric Equilibria of Substituted 2-Pyridone/2-Hydroxypyridine in the Gas and Aqueous Phases

Tautomeric Equilibria of Substituted 2-Pyridone/2-Hydroxypyridine in the Gas and Aqueous Phases

Ground-State Proton-Transfer Tautomer of the Salicylate Anion

The Thermodynamic and Kinetic Properties of 2-Hydroxypyridine/2-Pyridone Tautomerization: A Theoretical and Computational Revisit

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