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

Abstract

A number of bridgehead metalloidal-substituted phenylbicyclo[2.2.2]octyl and ( m- and p-)fluorophenylbicyclo[2.2.2]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 (σ 1 values) for a representative array of metalloidal substituents attached to an sp 3 hybridized carbon center. The implication of these results with respect to the physical interpretation of σ 1 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 bicyclo[2.2.2]- octane ring system. Factors determining α, β, γ and δ effects are briefly alluded to.