Electrostatic effects on ionization equilibria: MNDO study of proton and hydrogen transfer reactions of 5-fluoropentanoic acid

1985 ◽  
Vol 63 (5) ◽  
pp. 1068-1072 ◽  
Author(s):  
Zdenek Friedl
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Carboxylic Acids ◽  
Hydrogen Transfer ◽  
Opposite Sign ◽  
Substituent Effects ◽  
Transfer Reactions ◽  
Small Contribution ◽  
Bond Strengths ◽  
Ionization Equilibria

Relative proton transfer enthalpies δΔH0 and homolytic bond strengths δΔH0 (A—H) of sp and ap conformers of 5-fluoropentanoic acid, as well as some related aliphatic and 4-X-bicyclo[2.2.2]octane-1-carboxylic halogenoacids, have been calculated by the MNDO method. The results, together with literature data concerning the gas phase acidities, were compared with the prediction of the electrostatic theory. It is shown that the substituent effects on acidities of carboxylic acids are largely due to substituent interactions in the anions and only to a smaller extent to interactions in the neutral acids. A small contribution (about one-eighth to one-fourth as large in magnitude but of opposite sign) is possibly also made by substituent effects on homolytic bond strengths DH0 (A—H).

Electrostatic effects on ionization equilibria: An MNDO study of proton and hydrogen transfer reactions of 4-fluorobutylamine

1990 ◽  
Vol 55 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Zdeněk Friedl ◽  
Stanislav Böhm
Keyword(s):  
Hydrogen Transfer ◽  
Substituent Effects ◽  
Radical Cations ◽  
Transfer Reactions ◽  
Protonated Forms ◽  
Minor Part ◽  
Bond Strengths ◽  
Ionization Equilibria ◽  
A Minor ◽  
Gas Phase Basicities

The relative enthalpies of proton transfer δ ΔH0and homolytic bond strengths δDH0(B-H+) were calculated by the MNDO method for the sp and ap conformers of 4-flurobutylamine. The data obtained, along with the experimental gas phase basicities, are compared with the values predicted by the electrostatic theory. It is shown that the substituent polar effects FD on the basicities of amines are predominantly due to interactions in their protonated forms (X-B-H+) and/or radical-cations (X-B+.), those in the neutral species (X-B) playing a minor part. A contribution, which is considerably more significant in the sp conformer than in the ap conformer, arises probably also from substituent effects on the homolytic bond strength DH0(B-H+.

Electrostatic effects in ionization equilibria: An MNDO study of proton and hydrogen transfer reactions of 4-fluorobutanol

1990 ◽  
Vol 55 (12) ◽  
pp. 2880-2888 ◽  
Author(s):  
Zdeněk Friedl ◽  
Stanislav Böhm
Keyword(s):  
Hydrogen Transfer ◽  
Substituent Effects ◽  
Transfer Reactions ◽  
Molecular Orbital Calculations ◽  
Small Contribution ◽  
Bond Dissociation Energies ◽  
Bond Dissociation ◽  
Dissociation Energies ◽  
Ionization Equilibria ◽  
Reported Data

MNDO molecular orbital calculations have been carried out for sp and ap conformers of 4-fluorobutanol and some 4-X-bicyclo[2.2.2]octanols (X = F, Cl). The results are analyzed in terms of substituent effects on proton transfer enthalpies δ ΔH0 and homolytic bond dissociation energies δDH0 (A-H) and compared with the previously reported data for 5-fluoropentanoic acid and 4-fluorobutylamine. The results are further compared with the prediction of the electrostatic theory. It is shown that the substituent polar effect FD on the acidities of halogenoalcohols is largely due to substituent interaction in the anions and only to a smaller extent to interactions in the neutral alcohol. A small contribution (about one-tenth for the ap conformer) is probably also made by the substituent effects on homolytic bond dissociation energies DH0 (A-H).

Gas-phase proton-transfer reactions of the hydronium ion at 298 K

1979 ◽  
Vol 57 (12) ◽  
pp. 1518-1523 ◽  
Author(s):  
Gervase I. Mackay ◽  
Scott D. Tanner ◽  
Alan C. Hopkinson ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Transfer Reactions ◽  
Flowing Afterglow ◽  
Hydronium Ion ◽  
Proton Transfer Reactions

Rate constants measured with the flowing afterglow technique at 298 ± 2 K are reported for the proton-transfer reactions of H3O+ with CH2O, CH3CHO, (CH3)2CO, HCOOH, CH3COOH, HCOOCH3, CH3OH, C2H5OH, (CH3)2O, and CH2CO. Dissociative proton-transfer was observed only with CH3COOH. The rate constants are compared with the predictions of various theories for ion–molecule collisions. The protonation is discussed in terms of the energetics and mechanisms of various modes of dissociation.

An experimental study of the reactivity and relative basicity of the methoxide anion in the gas phase at room temperature, and their perturbation by methanol solvation

1982 ◽  
Vol 60 (20) ◽  
pp. 2594-2605 ◽  
Author(s):  
Gervase I. Mackay ◽  
Asit B. Rakshit ◽  
Diethard K. Bohme
Keyword(s):  
Proton Transfer ◽  
Gas Phase ◽  
Rate Constants ◽  
Solvent Free ◽  
Transfer Reactions ◽  
Free Proton ◽  
Proton Transfer Reactions ◽  
Intrinsic Reactivity ◽  
Relative Acidity ◽  
Methoxide Anion

Flowing afterglow measurements at 296 ± 2 K are reported which explore three aspects of the gas-phase acid–base chemistry of the methoxide anion. Firstly, the intrinsic reactivity of this ion has been determined from measurements of rate constants for solvent-free proton-transfer reactions with molecules more acidic than methanol including CH2=C=CH2, C6H5CH3, C2H5OH, C2H2, CH3CN, CH3COCH3, CH3CHO, CH3NO2, and HCN. Secondly, equilibrium constant measurements have been performed for solvent-free proton-transfer reactions which provide a gas-phase scale of acidities for these molecules relative to the acidity of methanol. Finally, rate constants were measured for the reactions of these acids with methoxide ions solvated with up to three molecules of methanol. The results establish trends in reactivity as a function of step–wise solvation when relative acidity is preserved and when a reversal occurs in the relative acidity upon solvation.

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