Proton affinities and gas-phase basicities: theoretical methods and structural effects

Deakyne, Carol A.

doi:10.1016/s1387-3806(03)00094-0

Cited by 107 publications

(86 citation statements)

References 64 publications

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“…It has been demonstrated that this approach has certain advantages over some other models aiming to interpret Brønsted acidities and basicities, as discussed in great detail recently by Deakyne, 48 and it was already successfully employed in the analysis of proton affinities, 49−51 deprotonation enthalpies 52−54 and hydride affinities. 55−57 Initial state effects of neutral bases are reflected in Koopmans' ionisation energies, 58 IE(B) n Koop , calculated in the frozen electron density and clamped atomic nuclei approximation (i.e., ionisation from the nth molecular orbital, counting the HOMO as the 1 st ).…”

Section: Computational Methodologymentioning

confidence: 92%

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

Radić¹,

Despotović²,

Vianello³

2012

Croat. Chem. Acta

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Abstract. M06-2X/6-311++G(2df,2pd)//M06-2X/6-31+G(d) computations were employed to investigate the intrinsic gas phase basicity of strained nitrogen heterocycles involving aziridine, azetidine, pyrrolidine and piperidine, together with their N-methyl and N-phenyl derivatives, NR(CH 2 ) n (n = 2-5; R = H, Me and Ph). Basicity constants were compared with the corresponding acyclic counterparts, NR(CH 3 ) 2 (R = H, Me and Ph), and were, based on triadic analysis, resolved into contributions mirroring features of both initial base and the final protonated form as well as their interplay, thus offering quantitative insight into the obtained results. In general, the N-methyl derivatives provided strongest bases investigated here, and, within each group of molecules, the basicity increased on going from three-to six-membered rings, consistent with a decrease in ring strain, with four-membered systems already surpassing or coming close to the basicity of the acyclic gauge molecule. Calculated basicities were found in a very good agreement with available experimental data, except for N-methylazetidine, where a remarkable discrepancy was revealed, suggesting that this system should be experimentally reassessed and its gas-phase basicity parameters revised. Triadic analysis showed different behaviour of individual contributions governing basicities, both among and within distinct families of molecules. It also convincingly demonstrated that, if a proper and a quantitatively accurate interpretation of observed basicity trends is desired, one should not rely only on concepts such as localized reactive hybrid orbitals (RHO) or thus derived nitrogen electron-donating ability (T. Ohwada et al., J. Org. Chem. 69 (2004) 7486), which take into account only properties of the initial base in question, but rather consider protonation reaction in its entirety. (doi: 10.5562/cca2121)

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Section: Computational Methodologymentioning

confidence: 92%

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

Radić¹,

Despotović²,

Vianello³

2012

Croat. Chem. Acta

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“…For this reason we performed triadic analysis in polysubstituted cyclopentadienes at the lower B3LYP/6-311 + G(d,p)//B3LYP/6-31G(d) level. As discussed by Deakyne recently, [24] the triadic analysis proved a superior approach for interpreting basicity and acidity than other models developed and used earlier. , što znači da se radi o rekordno jakim superkiselinama.…”

Section: Theoretical Frameworkmentioning

confidence: 99%

In Search of Ultrastrong Brønsted Neutral Organic Superacids: A DFT Study on Some Cyclopentadiene Derivatives

Vianello

Liebman

Maksić

2004

Chemistry A European J

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An efficient but reasonably accurate B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) computational procedure showed that pentasubstituted cyclopentadienes such as (CN)5C5H, (NO2)5C5H, and (NC)5C5H containing strongly electron-withdrawing groups are neutral organic superacids of unprecedented strength. The boldface denotes the atom attached to the cyclopentadiene framework. All of them exhibit prototropic tautomerism by forming somewhat more stable structures with C=NH, NO2H, and N=CH exocyclic fragments, respectively. The acidity (DeltaH(acid)) of these is lower, but only to a rather small extent. The DeltaH(acid) enthalpies of these last three tautomers are estimated to be 271, 276, and 282 kcal mol(-1), respectively. Hence, the most stable tautomers of (CN)5C5H and (NC)5C5H represent a legitimate target for synthetic chemists. On the other hand, (NO2)5C5H is less suitable for practical applications, because of its high energy density. The origin of the highly pronounced acidity of these compounds was analyzed by using the recently developed triadic formula. It is found that very high Koopmans' ionization energy (IE)n(Koop) of conjugate bases exerts a decisive influence on acidity. It follows as a corollary that the overwhelming effect leading to very high acidity is due to the properties of the final state. An alternative picture is offered by homodesmotic reactions, wherein the cyclic systems are compared with their linear counterparts. It is found that the acidity of cyclopentadiene (CP) is a consequence of aromatic stabilization in the CP- anion. The extreme acidity of pentacyanocyclopentadiene (CN)5C5H is due to aromatization of the five-membered ring and a strong anionic resonance effect in the resultant conjugate base. The neutral organic superacids predicted by the present calculations may help to bridge the gap between existing very strong acids and bases.

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“…Substitutional effects on proton affinities are well-known and substantial. [30][31][32][33][34][35][36] For a consistent set of comparisons, we computed the product structures and protonation energies of all the amines in Table 1. These computed results can be directly compared with tabulated gas-phase amine basicities, defined as the free energy of the protonation reaction, which we have taken from the NIST WebBook.…”

Section: Amine Protonationmentioning

confidence: 99%

Computational Comparison of the Reactions of Substituted Amines with CO₂

Mindrup

Schneider

2010

ChemSusChem

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Substituted amines are a popular choice as molecules to selectively react with and separate CO2 from gas mixtures. Such separations are of particular interest, for example, for CO2 separations for carbon capture and sequestration. It is desirable to tune amine–CO2 reaction energies to suit a particular separation. Herein, we use DFT‐B3LYP simulations to characterize the products and energetics of reactions of CO2 with a range of substituted amines, considering both 1:1 and 2:1 amine/CO2 reaction stoichiometries. The results show that by adjusting both the nature and the placement of functional groups, it is possible to tune reaction energies over a substantial range. Decomposition of the 2:1 reaction into separate carbamate and ammonium formation steps shows that the Brønsted basicity and Lewis basicity towards CO2 are largely uncorrelated and provide an independent means of tuning the overall reaction energies.

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Proton affinities and gas-phase basicities: theoretical methods and structural effects

Cited by 107 publications

References 64 publications

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

In Search of Ultrastrong Brønsted Neutral Organic Superacids: A DFT Study on Some Cyclopentadiene Derivatives

Computational Comparison of the Reactions of Substituted Amines with CO₂

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Proton affinities and gas-phase basicities: theoretical methods and structural effects

Cited by 107 publications

References 64 publications

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

Ring Strain and Other Factors Governing the Basicity of Nitrogen Heterocycles – An Interpretation by Triadic Analysis

In Search of Ultrastrong Brønsted Neutral Organic Superacids: A DFT Study on Some Cyclopentadiene Derivatives

Computational Comparison of the Reactions of Substituted Amines with CO2

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Computational Comparison of the Reactions of Substituted Amines with CO₂