ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
A new approach to the long-standing problem of interrelating meta and para substituent constants is presented. An analysis of the unified σ0-scale shows that the interrelation between σ40 and σ40/σ30 can 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 σ4n0 (σ4n0 - γ0)/(σ4n0 - 2γ0) = λ0 σ3n0 and σ4s0 = γ0 + λ0 σ3s0 are 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 σ0 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.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610080104
