Polar field-inductive parameters of some group IVB metalloidal substitutents: a 13C and 19F NMR study in the phenylbicyclo[2.2.2]octane ring system

A number of bridgehead metalloidal-substituted phenylbicyclo2.2.2]octyl and (m- and p-)fluorophenylbicyclo2.2.2]octyl derivatives have been synthesized and their ¹³C and ¹⁹F NMR spectra have been recorded. The appropriate ¹³C and ¹⁹F substituent chemical shifts of these stereochemically well-defined model systems, together with the known polar susceptibility parameters, provide a definitive scale of polar field-inductive parameters (σ₁ values) for a representative array of metalloidal substituents attached to an sp³ hybridized carbon center. The implication of these results with respect to the physical interpretation of σ₁ parameters is discussed. In addition, the previously reported results for alkyl groups in these systems have been re-evaluated in terms of possible through-bond effects involving orbitals of π symmetry of the bicyclo2.2.2]- octane ring system. Factors determining α, β, γ and δ effects are briefly alluded to.