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Hyperbolic Model for the meta – para interrelationship in benzene derivatives
Author(s) -
Reis JoãO Carlos R.,
Segurado Manuel A. P.,
De Oliveira Jaime D. Gomes
Publication year - 1995
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.610080104
Subject(s) - chemistry , substituent , benzene , lone pair , divergence (linguistics) , conjugate , computational chemistry , medicinal chemistry , stereochemistry , molecule , mathematical analysis , mathematics , organic chemistry , linguistics , philosophy
Abstract A new approach to the long‐standing problem of interrelating meta and para substituent constants is presented. An analysis of the unified σ 0 ‐scale shows that the interrelation between σ 4 0and σ 4 0 /σ 3 0can be modelled by a pair of conjugate rectangular hyperbolae, one for normal (n) and the other for special (s) substituents. The latter are characterized by a lone electron pair in the first atom. The equations σ 4n 0(σ 4n 0− γ 0 )/(σ 4n 0− 2γ 0 ) = λ 0 σ 3n 0and σ 4s 0= γ 0 + λ 0 σ 3s 0are derived and discussed in terms of Taft's separation of mesomeric and non‐mesomeric effects. Asymptotic values λ = 0.960 γ = −0.225 were obtained by non‐linear least rectangles fitting. A nonnegligible mesomeric contribution to σ 0 constants for normal substituents is predicted by the hyperbolic model. The present results are at variance with Exner's analysis of the meta ‐ para interrelationship in benzene compounds with normal substituents. This divergence is ascribed to opposite views concerning the role of the π‐inductive effect.