Anionic versus Neutral Protonation—An Ab Initio Analysis with a Triadic Formula

Maksić, Zvonimir B.; Vianello, Robert

doi:10.1002/1439-7641(20020816)3:8<696::aid-cphc696>3.0.co;2-c

Cited by 33 publications

(37 citation statements)

References 6 publications

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“…where ∆E is the change in the total energy of the reaction in Equation (2), which includes the zero-point energy and the finite temperature (298.15 K) correction, and ∆(pV) stands for the pressure-volume work term. A recently proposed novel triadic formula, Equation (4), enables estimation of the initial and final states' effects, as well as their interplay, on Brønsted basicities [15] and acidities [17] of organic compounds in the gas phase.…”

Section: Theoretical Frameworkmentioning

confidence: 99%

“…If we extend this approach to other corresponding pairs between amides and amines, triadic analysis offers an insight into the influence of the CH 3 -C=O group on the basicity of amino nitrogen directly attached to it. For that purpose we consider the set of Equations (15), (16), (17) and (18). .3] = -16.6 kcal·mol -1 (18) It is clear from the data provided by Equations 15-18 that the overall influence of the acetyl group is unfavourable such that the resulting nitrogen basicity of molecules 6-10 is reduced in relation to amines 1-5 unsubstituted by the acetyl group.…”

Section: Amides and Hydroxylaminementioning

confidence: 99%

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Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

2006

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An ab initio theoretical method based on a triadic formula has been employed to calculate changes in proton affinities (PAs) after sequential substitution of C-H by C-phenyl in methylamine and in the N-methyl component of N-methylacetamide. The overall objective was to investigate the cause of the recently reported unexpected basicity-enhancing effect of the N-trityl group in several amines and in acetamide. The triadic method indicates that the increase in PA from NH 3 to CH 3 NH 2 is principally due to destabilisation of the lone pair, compensated to some degree by a smaller bond energy term. The increasing PAs along the series CH 3 NH 2 , PhCH 2 NH 2 , Ph 2 CHNH 2 and Ph 3 CNH 2 are mainly due to an increasing relaxation energy effect following increasing phenyl substitution, supported by increasing bond energy terms. Introduction of para-methoxy substituents in tritylamine would be calculated to result in small incremental increases in PA, in agreement with experimental findings. The PA of tricyclohexylmethylamine (233.6 kcal·mol -1 ) is calculated to be similar to that of trimethoxytritylamine (233.5 kcal·mol -1 ), a consequence of the destabilisation of the lone pair on nitrogen by the three bulky cyclohexyl groups. Results for acetamide indicate that protonation on oxygen is

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Section: Theoretical Frameworkmentioning

confidence: 99%

Section: Amides and Hydroxylaminementioning

confidence: 99%

Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

2006

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“…It is embodied in the triadic formula based on dissection of the (de)protonation process into three stages corresponding to the initial, intermediate and final state events. 25,26 Let us consider the acidic dissociation of the proton as a reverse reaction: protonation of the anionic conjugate base. One should keep in mind that in this case the final state in deprotonation becomes the initial state in the protonation of the anions.…”

Section: Introductionmentioning

confidence: 99%

“…Consistent application of this model has conclusively shown that carboxylic acids X-COOH are more acidic than alcohols X-OH (X ¼ H, CH 3 , F, CF 3 ), because of considerably larger Koopmans' ionization energies. 26 To put it succinctly, the enhanced acidity of carboxylic acids X-COOH (X ¼ H, CH 3 , F, CF 3 ) is a consequence of the final state (anionic) features.…”

Section: Introductionmentioning

confidence: 99%

Gas‐phase acidity ofpara‐substituted benzoic acids—a triadic analysis of substituent effects

Vianello

Maksić

2005

J of Physical Organic Chem

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Deprotonation energies in vacuo of a large number of para-substituted benzoic acids encompassing a wide variety of substituents [F, Cl, Br, CH 3 , C(CH 3 ) 3 , CH --CH 2 , C ---CH, CHO, COOH, CF 3 , BH 2 , B(CH 3 ) 2 , NH 2 , N(CH 3 ) 2 , OH, OCH 3 , SH, CN and NO 2 ] were studied by a reliable ab initio method. It is shown by using a triadic formula analysis that the enhanced acidity of these compounds is a consequence of the final state as a rule, i.e. it is a result of the greater stability of the conjugate bases. There are just a few exceptions to this rule, involving C(CH 3 ) 3 , OCH 3 , OH and SH substituent groups. In the last two cases molecules deprotonate at the O and S substituent atoms, respectively. The ring-substituted pentacyano derivative of benzoic acid was also examined. It is shown that it exhibits highly pronounced acidity owing to a strong anionic resonance effect in the resulting final state anion.

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“…[16,17] In addition, theory can offer a simple and intuitively appealing interpretation of the acidity features. [18,19] Recently, a strong emphasis has been placed on the design of very potent neutral organic superacids in silico. [20Ϫ23] The largest body of theoretical results, however, refers to the gas phase; estimates of acidity in solutions are scarce.…”

Section: Introductionmentioning

confidence: 99%

The Acidity of Brønsted CH Acids in DMSO − The Extreme Acidity of Nonacyanocyclononatetraene

Vianello

Maksić

2004

Eur J Org Chem

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The gas-phase (GP) acidity of a large variety of CH organic acids is studied by a carefully selected B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d) theoretical model. Acidities are mirrored by the proton affinities of the corresponding conjugate bases. A very good agreement with available experimental data is achieved. It is concluded that the model applied has a high predictive value and that theoretical PA(anion) GP values can be used instead of measured data in cases where experiments are not feasible or not performed. It is shown, employing the isodensity polarized continuum model (IPCM), that there is a good linear relationship between the enthalpies of the proton-transfer reactions in

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Anionic versus Neutral Protonation—An Ab Initio Analysis with a Triadic Formula

Cited by 33 publications

References 6 publications

Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

Basicity of Amines in the Gas Phase – Analysis of the Base‐Strengthening Effect of an N‐Trityl Group by Use of a Triadic Formula

Gas‐phase acidity ofpara‐substituted benzoic acids—a triadic analysis of substituent effects

The Acidity of Brønsted CH Acids in DMSO − The Extreme Acidity of Nonacyanocyclononatetraene

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