Influence of connector groups on the interactions of substituents with carbon-centered radicals

High-level G3X(MP2)-RAD calculations have been carried out to examine the effect of interposing a “connector” group (W) on the interaction between a substituent (X) and the radical center in carbon-centered radicals (•CH₂–W–X). The connector groups include −CH₂–, −CH═CH–, −C≡C–, −p-C₆H₄–, −m-C₆H₄–, and −o-C₆H₄–, and the substituents include H, CF₃, CH₃, CH═O, NH₂, and CH═CH₂. Analysis of the results is facilitated by introducing two new quantities termed radical connector energies and molecule connector energies. We find that the −CH₂– connector effectively turns off π-electron effects but allows the transmission of σ-electron effects, albeit at a reduced level. The effect of a substituent X attached to the −CH═CH– and −C≡C– connector groups is to represent a perturbation of the effect of the connector groups themselves (i.e., CH═CH₂ and C≡CH)