A novel electrostatic approach to substituent constants: doubly substituted benzenes

Suresh, C. H. ; Gadre, Shridhar R. (1998) A novel electrostatic approach to substituent constants: doubly substituted benzenes Journal of the American Chemical Society, 120 (28). pp. 7049-7055. ISSN 0002-7863

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Official URL: http://pubs.acs.org/doi/abs/10.1021/ja973105j

Related URL: http://dx.doi.org/10.1021/ja973105j


The most negative-valued molecular electrostatic potential (MESP) minimum (Vmin) observed over the benzene ring is proposed as a sensitive quantity for the analysis of the electronic perturbations due to the substituents attached to it. MESP topography of 45 doubly substituted benzenes is mapped at HF/6-31G∗∗ level for an appraisal of this proposition. The Vmin values are seen to clearly reflect the changes due to the different orientations (para, meta, and ortho) and conformations of the substituents and different mechanisms of electron donation or withdrawal. Good linear correlations are obtained with Vmin and the experimentally determined s values of the ortho- and meta-disubstituted benzenes. New quantities, Dp, Dm, and Do, introduced in this work as the substituent pair-constants respectively for the para, meta, and ortho arrangements, provide a quantitative measure of the simultaneous effect of two substituents over the aromatic nucleus. The predictive power of these quantities is checked in the case of some triply substituted benzenes using an equation Vmin = Vben + ∑ΔVmin(mono) - ∑Dp - ∑Dm - ∑Do where Vben is the MESP minimum of benzene and ΔVmin(mono) is the difference between the monosubstituted benzene Vmin and Vben. These predicted values are in fairly good agreement with the MESP values obtained at HF/6-31G∗∗ level.

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