Revised Substituent Entropy Constants σ_S° for Di- and Tri-Substituted Benzene Derivatives, and Their Applications for Substrates Having Two Substituted Phenyl Rings

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The revised substituent entropy constants σ_S° representing both dispersion and repulsion interactions are expressed by the next equations; σ_S°(12)=0.859Σσ_S°(mono)-0.011;σ_S°(13)=0.894Σσ_S°(mono)-0.013;σ_S°(14)=0.905Σσ_S°(mono)-0.022; σ_S°(123)=0.779Σσ_S°(mono)-0.021; σ_S°(124)=0.765Σσ_S°(mono)-0.007; σ_S°(135)=0.817Σσ_S°(mono)-0.033; where the correction due to the symmetry number, n×Rln2, should be introduced optionally. The descriptors σ_S° of the substrates having two substituted phenyl rings-namely, biphenyls, diphenyl ethers, -amines, -methanes, sulfides and benzophenones-could be determined by the joint use of the next equations; σ_S°(1234)=0.704Σσ_S°(mono)-0.024;σ_S°(1235)=0.702Σσ_S°(mono)-0.018; σ_S°(1245)=0.706Σσ_S°(mono)-0.023; σ_S°(penta)=0.618Σσ_S°(mono)-0.012;σ_S°(hexa)=0.570Σσ_S°(mono)-0.012.Observed results suggest that the concept of isosterism could probably be related to a similar level of dispersion and repulsion interactions between receptor and substrate.