Polarity of Elements and Radicals Measured in Terms of a Logarithmic Function of the Ionization Constant.

Derick, C. G.

doi:10.1021/ja02220a018

Cited by 20 publications

(12 citation statements)

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“…On the one hand, effects of individual substituents were quantitatively estimated 5-8 and expressed by a scale of constants denoted s I or s F ; good evidence was obtained that they remain proportional and can be transferred from one reaction to another. 7,9,10 On the other hand, simplified theories were advanced which either express the I-effect in terms of electrostatic repulsion or attraction, 11,12 or describe its propagation along the bonds 13 with a possible similarity to an electric network. 14 Pros and cons of the two theories have been discussed, 15,16 but recently the opinion prevails that they should be regarded only as two very approximate models.…”

Section: Introductionmentioning

confidence: 99%

Re-evaluation of the inductive effect in isolated molecules and in solution

Exner

Nau

2000

J. Phys. Org. Chem.

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The classical concept of inductive effect based originally on dissociation constants in water was revisited on isolated molecules in the gas phase. It then has a strict thermodynamic meaning of ΔHo(g) of an isodesmic reaction and can be calculated separately in the neutral molecules of acids (bases) and in anions (cations). Eight different reactions were investigated in which tradition assumes a purely inductive effect. Quantitative estimation was based on the known gas‐phase enthalpies of ionization, ΔionHo(g), and gas‐phase enthalpies of formation, ΔfHo(g); some lacking values of the latter were substituted by calculations at the MP2/6–31+G** or RHF/6–31+G** level. Substituent effects in neutral molecules are not negligible, particularly in smaller molecules, but are qualitatively different from the common scale of inductive effect and cannot at present be described in terms of any simple theory. The concept of inductive effect is to be reserved just for the energy difference between an ion and the respective neutral molecule. It can be modeled as the energy of interaction between the given substituent and a positive or negative charge but it is quantitatively predicted in terms of electrostatics (Kirkwood–Westheimer theory) only with some considerable disagreements. In water, this effect is strongly attenuated, differently in different classes of compounds; this attenuation can be in a qualitative accord with the electrostatic theory. Copyright © 2000 John Wiley & Sons, Ltd.

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Section: Introductionmentioning

confidence: 99%

Re-evaluation of the inductive effect in isolated molecules and in solution

Exner

Nau

2000

J. Phys. Org. Chem.

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“…7 in Ref 8). For the first orientation or for text-book purposes, the statement is sufficient that a more remote substituent has a smaller effect; even the simple rule [47][48][49] that it is reduced to one third by any further bond is still valid.…”

Section: Discussionmentioning

confidence: 99%

“…The alternative theory, [47][48][49] called most properly sigma-inductive, does not allow the inductive effect to be calculated explicitly. It only describes its dependence on structure for a given substituent and a given reaction center; in terms of Eqn.…”

Section: Transmission Through Bonds or Through Space Theoretical Concmentioning

confidence: 99%

The inductive effect: theory and quantitative assessment

Exner¹

1999

J. Phys. Org. Chem.

102

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The concept of the inductive effect is defined in terms of thermodynamics and its quantitative estimation is reviewed. The electrostatic (through-space) and sigma-inductive (through-bond) theories are confronted and experimental proofs evaluated, with the result that both theories are very approximate and neither is in principle correct. The inductive effect in isolated molecules (acids, bases, anions, cations) is estimated separately by means of isodesmic reactions.

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“…Both were first suggested by Derick. 1 The inductive effect involves the successive polarization of the bonds between X and Y. The initial electrical effect is decreased by passage through each bond by a fraction called the falloff factor, f, which is reported to have a value of 0.33-0.36.…”

Section: Introductionmentioning

confidence: 99%

“…The initial electrical effect is decreased by passage through each bond by a fraction called the falloff factor, f, which is reported to have a value of 0.33-0.36. [1][2][3] The field effect is propagated directly through space, it is a function of the distance r between X and Y and of the cosine of the angle θ between the XG bond and the XY distance. 4, 5 Classical electrostatics requires the dependence on cosine θ when the substituent is a dipole.…”

Section: Introductionmentioning

confidence: 99%

The mode of transmission of electrical effects †

Charton¹,

Charton²

1999

J. Chem. Soc., Perkin Trans. 2

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The dependence of substituent electrical effect transmission on substituent-reaction site distance and on the charge on reactant and product or transition state has been studied in the systems X-G-Y and X-Y where X is a variable substituent, Y a reaction site, and G a skeletal group. Reaction types studied were molecule-molecule (MM), molecule-ion (MI), and molecular ionization (Mi). MM reactions include proton transfer equilibria (pK a 's) of compounds with Y = CO 2 H, OH, SO 2 NH 2 , NR 2 H ϩ , azarenes, PO 2 (OH) Ϫ , and SH; gas phase ∆G acid values for Y = CO 2 H and OH, and proton affinities for NR 2 H ϩ , proton transfer reaction rates for XGCO 2 H with Ph 2 CN 2 , and hydrogen bonding equilibria for XGCN (pK HB ). MI's include rates of base catalyzed ester hydrolysis, nucleophilic substitution of PhCOCH 2 Br by XGCO 2 Ϫ , and protodetritiation of T-substituted arenes. Mi reactions were solvolyses of XGCHLgMe (Lg is a leaving group) and XGCMe 2 Cl. The measure of electrical effect magnitude used was L, the coefficient of the localized (field and/or inductive) effect obtained from correlation of appropriate data sets with linear free energy relationships. The substituent-reaction site distance was parameterized by n, the number of bonds between the substituent and the nearest atom of the reaction site undergoing bond change (Y 1 ). Correlations of L with 1/n 2 and 1/n; and of log |L| with log n by simple linear regression analysis determined the dependence of L on n. Data sets with very large values of θ, the angle between the X-G bond and the line joining X and Y 1 , were excluded. Data in aqueous-organic solvent mixtures can be combined into a single data set regardless of the solvent composition, probably due to preferential solvation by water. The results do not agree with the Kirkwood-Westheimer model for MI, Mi, and some MM reactions all of which show a dependence on 1/n rather than 1/n 2 . They support a modified field effect as the mode of transmission. This model differs from the Kirkwood-Westheimer model m seeming to depend on the charge difference between initial and final states.

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Polarity of Elements and Radicals Measured in Terms of a Logarithmic Function of the Ionization Constant.

Cited by 20 publications

References 0 publications

Re-evaluation of the inductive effect in isolated molecules and in solution

Re-evaluation of the inductive effect in isolated molecules and in solution

The inductive effect: theory and quantitative assessment

The mode of transmission of electrical effects †

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