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

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).

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

Canadian Journal of Chemistry ◽

10.1139/v85-181 ◽

1985 ◽

Vol 63 (5) ◽

pp. 1068-1072 ◽

Cited By ~ 4

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).

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

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19900001 ◽

1990 ◽

Vol 55 (1) ◽

pp. 1-9 ◽

Cited By ~ 1

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+.

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