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Inductive effect of uncharged groups: dependence on electronegativity
Author(s) -
Exner Otto,
Böhm Stanislav
Publication year - 2006
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1093
Subject(s) - isodesmic reaction , chemistry , electronegativity , substituent , inductive effect , polar , computational chemistry , atom (system on chip) , density functional theory , conjugated system , chemical polarity , ionization , crystallography , stereochemistry , organic chemistry , quantum mechanics , polymer , molecule , ion , physics , computer science , embedded system
Abstract Substituent effects in rigid non‐conjugated systems were followed on the series of 3‐substituted 1‐fluoro‐bicyclo[1.1.1]pentanes and 2‐substituted 1‐fluoroethanes in the fixed ap conformation. Their energies were calculated within the framework of the density functional theory at the B3LYP/6‐311++G(3df,3pd)//B3LYP/6‐311++G(3df,3pd) level and the substituent effects were expressed in terms of isodesmic homodesmotic reactions. The results were confirmed by the energies of 1,4‐disubstituted bicyclo[2.2.2]octanes reported in the literature and calculated at a lower level. Interaction of two common substituents of low or medium polarity cannot be described as the classical inductive effect by one term, proportional in all series, but an additional parameter is necessary, which depends only on the first atom of the substituent and may be identified with its electronegativity. The second term decreases with the distance more steeply than the first term and is always much less important. Nevertheless its statistical significance was proved by several sensitive tests at the highest level used in statistics. When one of the substituents is charged (or at least strongly polar as NO 2 or CN), the first term is much increased and the second becomes less significant or insignificant. Therefore, the standard definition of the inductive effect with a uniform, universally valid constant can be retained as far as one treats only the ionization equilibria, both in solution and in the gas phase, or kinetics with a strongly polar transition state. In contrast to the firm statistical proofs, the physical meaning of the electronegativity term was not established. Any relation to various group electronegativities does not exist, similarity to the 13 C NMR shifts is merely qualitative. Copyright © 2006 John Wiley & Sons, Ltd.