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 ((•)CH(2)-W-X). The connector groups include -CH(2)-, -CH═CH-, -C≡C-, -p-C(6)H(4)-, -m-C(6)H(4)-, and -o-C(6)H(4)-, and the substituents include H, CF(3), CH(3), CH═O, NH(2), and CH═CH(2). Analysis of the results is facilitated by introducing two new quantities termed radical connector energies and molecule connector energies. We find that the -CH(2)- 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═CH(2) and C≡CH).