Rate-equilibrium relationships for the deprotonation of 4-phenacylpyridines and 4-phenacylpyridinium cations

Stefanidis, Dimitrios; Bunting, John W.

doi:10.1021/ja00164a044

Cited by 23 publications

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“…[2] is considerably smaller than that found for any of the other cationic acids in Table 2. If one uses p = 1.14 for the tertiary benzyldimethylammonium cations as a reference, then p = 0.18 from eq.…”

Section: Discussioncontrasting

confidence: 61%

“…If one uses p = 1.14 for the tertiary benzyldimethylammonium cations as a reference, then p = 0.18 from eq. [2] indicates only a small fractional decrease in the effective charge upon the cationic nitrogen atom in 6 upon enolate formation. This result suggests a limited contribution from resonance contributors such as the N-benzyl analog of 2c to the electronic structure of the conjugate base, although the electronic absorption spectrum (X, , , = 445 nm) of this species is only readily rationalized in valence bond terms via a contribution from 2c to the electronic structure of the resonance stablized enolate species.…”

Section: Discussionmentioning

confidence: 99%

“…The relatively high acidities of the ketones 1 and 3 can be thermodynamic and kinetic acidities of these ketones, and detraced to the resonance stabilization provided by the contriburived Bronsted slopes for these reactions (1)(2)(3)(4). These investors 2a-2c and 4a-4c, respectively, to the electronic structures ' (2)) displays a long wavelength electronic absorption maximum that is consistent with a highly delocalized electronic structure.…”

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confidence: 97%

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Thermodynamic and kinetic acidities of N-(substituted benzyl) 4-phenylacetylpyridinium cations in aqueous solution

Bunting¹,

Aubin²

1991

Can. J. Chem.

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. Can. J. Chem. 69, 945 (1991). The pKa values for the deprotonation of a series of eight 1-(X-benzy1)-4-phenylacetylpyridinium cations (6) have been measured in aqueous solutions of ionic strength 0.1 at 25°C: pKa = -0 . 1 8~ + 8.91. The pseudo-first-order rate constants for deprotonation of these carbon acids have been measured over the range pH = 11-13, and have been found to display kinetic saturation effects that are consistent with the addition of hydroxide ion to the carbonyl group (pK,) as the product of kinetic control upon basification of neutral aqueous solutions of these pyridinium cations, with the subsequent transformation of this anionic hydrate to the thermodynamically more stable enolate conjugate base. Analysis of the pH-rate profiles gives substituent effects upon pK, (p = -0.19) and upon the second-order rate constant (koH (p = 0.09)) for deprotonation of 6 by hydroxide ion.Key words: carbon acids, deprotonation, pK,, kinetics, substituent effects. The isomeric ketones 1 (pK, = 9.02 for X = H (1)) and 3 (pK, tigations have been instrumental in the development of a useful = 7.66 for X = H (2)) readily undergo deprotonation in aqueous empirical modification to the Marcus relationship as it is applied solution to form their enolate conjugate bases (2 and 4, respecto the study of rate-equilibrium relationships for the deprotonatively). In previous studies, we explored the influence of substittion of carbon acids (1, 2 , 4 , 5 ) . uents in the phenyl ring of each of 1 and 3 upon both theThe relatively high acidities of the ketones 1 and 3 can be thermodynamic and kinetic acidities of these ketones, and detraced to the resonance stabilization provided by the contriburived Bronsted slopes for these reactions (1-4). These investors 2a-2c and 4a-4c, respectively, to the electronic structures For personal use only.

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Section: Discussioncontrasting

confidence: 61%

Section: Discussionmentioning

confidence: 99%

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confidence: 97%

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Thermodynamic and kinetic acidities of N-(substituted benzyl) 4-phenylacetylpyridinium cations in aqueous solution

Bunting¹,

Aubin²

1991

Can. J. Chem.

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“…We felt that similar insight into the electronic structure of the conjugate bases of the corresponding sulfonyl-activated carbon acids (2, 6 , and 7) would also be of interest in view of the wide use of sulfonyl-stabilized carbanions as reagents in synthetic organic chemistry. Furthermore, in conjunction with our previous study of substituent effects upon the acidities of the ketones 1, 4, and 5 (7), such data would allow a detailed comparison of substituent effects upon the acidities of these two closely related series of carbonyl-and sulfonyl-activated carbon acids in aqueous solution. In particular, we felt that such a comparison might provide quantitative insight into the saturation of resonance effects that is commonly observed upon the acidities of carbon acids when successive activating substituents are introduced.…”

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confidence: 90%

“…The current paper reports the synthesis and acidities of a wide range of ring-substituted 4-arylsulfonylmethylpyridines (6) and their N-methyl cations (2) and also N-(substituted benzyl) 4-phenylsulfonylmethylpyridinium cations (7). In addition, the pK, values were measured for several other sulfonylmethylpyridinium cations (8)(9)(10)(11) in aqueous solution.…”

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confidence: 99%

The acidities of 4-arylsulfonylmethylpyridines and N-methyl and N-benzyl 4-arylsulfonylmethylpyridinium cations in aqueous solution

Wodzinski¹,

Bunting²

1992

Can. J. Chem.

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. The pK, values for the deprotonation of a series of 4-(X-phenylsulfonylrnethy1)pyridines (6) (pK, = 19.89 (X = H); p = 3.0) were determined in aqueous dirnethyl sulfoxide solutions at 25°C using the Hoq acidity function. The pK, values were also measured for the corresponding series of N-methyl 4-(X-phenylsulfonylmethy1)pyridiniurn cations (2) (pK, = 11.27 (X = H); p = 1.45) and also for a series of N-(X-benzyl) 4-phenylsulfonylrnethylpyridinium cations (7) (pK, = 10.70 (X = H); p = 0.65) in aqueous solution (ionic strength 0.1 at 25'C). Comparison of the substituent effects upon the pK, values of the sulfonyl-activated carbon acids 2, 6 , and 7 with the substituent effects upon the pK, values of the corresponding three series of ketones gives insight into the electron-density distribution in the carbanionic conjugate bases of sulfone and ketone carbon acids. Extrapolation of a linear free energy relationship between the pK, values of neutral sulfones and ketones allows the estimation of pK, = 28.7 for the deprotonation of methyl phenyl sulfone in aqueous solution. STEFAN WODZINSKI et JOHN W. BUNTING. Can. J. Chern. 70, 2635 (1992. OpCrant i 25"C, dans des solutions de dimCthylsulfoxyde aqueuses et faisant appel i la fonction d'aciditi HOq, on a dCterminC les valeurs de pK, pour la dCprotonation d'une sCrie de 4-(X-phenylsulfonylrnCthy1)pyridines (6) (pK, = 19,89 (X = H); p = 3,O). On a aussi mesurC les valeurs des pK, pour la strie correspondante des cations N-mCthyl 4-(XphCnylsulfonylmCthy1)pyridiniurn (2) (pK, = 11,27 (X = H); p = 1,45) ainsi que pour une sCrie de cations N-(X-benzyl) 4-(X-phCnylsulfonylmCthy1)pyridinium (7) (pK, = 10,70 (X = H); p = 0,65) en solution aqueuse (force ionique de 0 , l i 25°C). Une comparaison des effets de substituants sur les valeurs de pK, des acides carbonks 2, 6 et 7, activCs par le sulfonyle, avec les effets de substituants sur les valeurs des pK, des trois sCries de cCtones correspondantes Cclaire notre comprChension de la distribution de la densite Clectronique dans les bases carbanioniques conjuguCes des acides carbonks de sulfones et de cCtones. Une extrapolation de la relation d'knergie libre linCaire entre les valeurs de pK, des sulfones et des cCtones neutres perrnet dlCvaluer i 28,7 la valeur du pK, pour la dCprotonation de la methyl phCnyl sulfone, en solution aqueuse.[Traduit par la redaction]There have been relatively few quantitative measurements of the thermodynamic acidities of sulfonyl-activated carbon acids in aqueous solution. The acidities of bis(methylsulfonyl)methane ((CH,SO2),CH2, pK,, = 12.5 (1-3)) and bis(phenylsulfonyl)methane ((C6H5S02),CH,, pK, = 1 1.2 1 (1)) have been measured in water, and related cyclic 1,3-disulfones have been found, depending upon ring size, to be up to 1.5 pK, units more acidic (eight-membered ring) or less acidic (five-membered ring) than these acyclic sulfones (1). a-Methylation of disulfones leads to a significant decrease in acidity ((C,H,SO,),CHR, pK, = 12.20 for R = H, pK, = 14.56 for R = CH, (3a); (C6H5S02)2CHR, pK,...

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Theoretical studies on the transition-state imbalance in malononitrile anion-forming reactions in the gas phase and in water

Lee

Kim

Lee

et al. 1997

J. Phys. Org. Chem.

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Rate-equilibrium relationships for the deprotonation of 4-phenacylpyridines and 4-phenacylpyridinium cations

Cited by 23 publications

References 0 publications

Thermodynamic and kinetic acidities of N-(substituted benzyl) 4-phenylacetylpyridinium cations in aqueous solution

Thermodynamic and kinetic acidities of N-(substituted benzyl) 4-phenylacetylpyridinium cations in aqueous solution

The acidities of 4-arylsulfonylmethylpyridines and N-methyl and N-benzyl 4-arylsulfonylmethylpyridinium cations in aqueous solution

Theoretical studies on the transition-state imbalance in malononitrile anion-forming reactions in the gas phase and in water

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