Solvent Basicity

Benoit, R. L.; Louis, C.

doi:10.1016/b978-0-12-433805-0.50008-2

Cited by 4 publications

(3 citation statements)

References 115 publications

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“…, (2) a calorimetric scale based on an N−H acid, (such as pyrrole) which poses no conformational problems and based on the δΔ H solv of Laynez et al , (3) a spectroscopic scale constructed from a phenol acid such as that of ΔΔν̃(1)−(2) of Laurence et al. , (4) a spectroscopic scale based on an N−H acid (4-nitroaniline), such as that of ΔΔν̃(3)−(5) of Laurence et al , and (5) the δΔ H g→solv values for SO 2 and I 2 reported by Benoit and Louis …”

Section: Resultsmentioning

confidence: 99%

On Solvent Basicity: Analysis of the SB Scale

et al. 1997

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The solvent basicity (SB) scale, introduced by Catalán et al. in 1996, was compared with theoretical data (V min and εmo(Vmin)), calculated at the HF-SCF 6-31G** level, and with experimental data (ΔH f of Arnett, δΔH solv of Laynez, ΔΔν̃(1)−(2) and ΔΔν̃(3)−(5) of Laurence, and ΔH g→solvent for SO2 and I2 of Benoit and Louis). The fact a SB scale is a family-independent scale results in no grouping of the solvents in parallel lines. As also shown by the results, a basicity scale constructed around a standard phenolic Brönsted acid (R-OH) such as 4-nitrophenol or 4-fluorophenol is more correct than one based on an unsubstituted amine such as 4-nitroaniline. The SB scale has a near-unity covalent-to-electrostatic ratio, so it is sensitive to both covalent and electrostatic interactions and hence approaches closely the requirements for a general basicity scale.

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Section: Resultsmentioning

confidence: 99%

On Solvent Basicity: Analysis of the SB Scale

et al. 1997

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“…The term Δ G ° tr (H + ) is the free energy of transfer of the proton from water to DMSO (−4.8 kcal/mol, an average of two values, −4.5 6a and −5.0 6b kcal/mol), Δ G ° f (H • ) g is the free energy of formation of the hydrogen atom taken as 48.6 kcal/mol,6c and Δ G ° sol (H • ) is the free energy of solvation of the hydrogen atom (−5.7 kcal/mol 6d ), assumed to be the same as that of the hydrogen molecule. Δ G ° sol (AH) and Δ G ° sol (A • ) in the equilibrium, AH ⇄ A • + H • are assumed to be equal for large organic molecules.…”

Section: Introductionmentioning

confidence: 99%

“…To compare the free energy (Δ G °) BDE values (eq 8) with Δ H ° BDE values, an entropy term for the formation of the hydrogen atom, T Δ S °, must be included. It is assumed that the entropy for (A−H) g is equal to that of (A • ) g and that Δ S ° ≃ S °(H • ) g = 27.4 eu. 6c,e The total T Δ S ° contribution to BDE, therefore, is 8.2 kcal/mol. Combining the values of terms in eq 8 provides eq 10 with a value of 56 kcal/mol for constant ( C ) when the oxidation potentials of the conjugate anions { E ox (A - ) s} are measured versus the standard hydrogen electrode (SHE) 4b…”

Section: Introductionmentioning

confidence: 99%

Equilibrium Acidities and Homolytic Bond Dissociation Energies of Acidic C−H Bonds in α-Arylacetophenones and Related Compounds

et al. 2002

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The equilibrium acidities (pK(AH)s) and the oxidation potentials of the congugate anions [E(ox)(A(-))s] were determined in dimethyl sulfoxide (DMSO) for eight ketones of the structure GCOCH(3) and 20 of the structure RCOCH(2)G, (where R = alkyl, phenyl and G = alkyl, aryl). The homolytic bond dissociation energies (BDEs) for the acidic C-H bonds of the ketones were estimated using the equation BDE(AH) = 1.37pK(AH) + 23.1E(ox)(A(-)) + 73.3. While the equilibrium acidities of GCOCH(3) were found to be dependent on the remote substituent G, the BDE values for the C-H bonds remained essentially invariant (93.5 +/- 0.5 kcal/mol). A linear correlation between pK(AH) values and [E(ox)(A(-))s] was found for the ketones. For RCOCH(2)G ketones, both pK(AH) and BDE values for the adjacent C-H bonds are sensitive to the nature of the substituent G. However, the steric bulk of the aryl group tends to exert a leveling effect on BDEs. The BDE of alpha-9-anthracenylacetophenone is higher than that of alpha-2-anthracenylacetophenone by 3 kcal/mol, reflecting significant steric inhibition of resonance in the 9-substituted system. A range of 80.7-84.4 kcal/mol is observed for RCOCH(2)G ketones. The results are discussed in terms of solvation, steric, and resonance effects. Ab initio density functional theory (DFT) calculations are employed to illustrate the effect of steric interactions on radical and anion geometries. The DFT results parallel the trends in the experimental BDEs of alpha-arylacetophenones.

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Hydrogen‐bonding. Part 4. An analysis of solute hydrogen‐bond basicity, in terms of complexation constants (log K), using F₁ and F₂ factors, the principal components of different kinds of basicity

Abraham

Grellier

Prior

et al. 1989

J of Physical Organic Chem

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The principal components factors F1 and F2 in the equation have been used to obtain S1 and S2 values for sets of hydrogen‐bond bases against 32 reference acid/solvent systems. The constants S1 and S2 define an angle θ = tan−1 S2/S1 that is a measure of the electrostatic:covalent bonding ratio in the hydrogen‐bond complex. It is shown that θ can vary from 53 (4‐fluorophenol in CH2Cl2)to 86 degrees (Ph2NH in CCl4) depending on the reference acid and solvent. This variation in θ can lead to family dependent behaviour in plots of log K for bases against a given reference acid system vs log K for bases against another reference acid system, and precludes the construction of any general scale of hydrogen‐bond basicity using log K values. Amongst a quite wide range of reference acid/solvent systems θ varies only from 64 to 73 degrees, and for bases against these reference systems a ‘reasonably general’ scale could be set up. Such a scale could be extended to bases against reference acid/solvent systems outside the 64–73 degree range provided that certain classes of base (e.g. pyridines, alkylamines) were excluded from the additional reference acid/solvent systems.

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Solvent Basicity

Cited by 4 publications

References 115 publications

On Solvent Basicity: Analysis of the SB Scale

On Solvent Basicity: Analysis of the SB Scale

Equilibrium Acidities and Homolytic Bond Dissociation Energies of Acidic C−H Bonds in α-Arylacetophenones and Related Compounds

Hydrogen‐bonding. Part 4. An analysis of solute hydrogen‐bond basicity, in terms of complexation constants (log K), using F₁ and F₂ factors, the principal components of different kinds of basicity

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Solvent Basicity

Cited by 4 publications

References 115 publications

On Solvent Basicity: Analysis of the SB Scale

On Solvent Basicity: Analysis of the SB Scale

Equilibrium Acidities and Homolytic Bond Dissociation Energies of Acidic C−H Bonds in α-Arylacetophenones and Related Compounds

Hydrogen‐bonding. Part 4. An analysis of solute hydrogen‐bond basicity, in terms of complexation constants (log K), using F1 and F2 factors, the principal components of different kinds of basicity

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Hydrogen‐bonding. Part 4. An analysis of solute hydrogen‐bond basicity, in terms of complexation constants (log K), using F₁ and F₂ factors, the principal components of different kinds of basicity