A Self-Consistent and Cross-Checked Scale of Spin-Delocalization Substituent Constants, the ?*JJ Scale

Article abstract of DOI:10.1021/jo00048a048

On the basis of the 19F NMR data of substituted α,β,β-trifluorostyrenes and the rate constants of their thermal cycloaddition reactions, a self-consistent and cross-checked scale of spin-delocalization substituent constants ?^*_JJ is proposed for 21 para-substituents and for 10 meta-substituents.By means of adopting different ρ_mb values, three methods for the calculation of the ?^*_JJ values at five different temperatures and their averaged values are presented.It has been shown that at each temperature and within a range of ρ_mb values from -0.20 to -0.40 the same set of ?^* constants are obtained from these three methods.There are seven advantages to the ?^*_JJ approach, including the fact that the reaction is exceptionally clean, a tailor-made polar parameter ?_mb is used in the dual-parameter equation, and the validity of the approach is strongly supported by the meta substituent effect which is independent of the polar effect.Some radical reactions, EPR data of substituted benzyl radicals, and bond dissociation energies are reexamined by using the ?^*_JJ in conjunction with polar ? constants in dual-parameter equations.