A theoretical scale of substituent resonance parameters (σR°)

Abstract

It is shown that molecular orbital calculations at the ab-initio level can provide a scale of resonance effects in good agreement with experimental values appropriate for the gas-phase or non-polar solvents. Using monosubstituted ethylenes as models allows calculations for a wide range of substituents on a split-valence basis. Values of σ_R° have been calculated for more than 40 common substituents, including some for which experimental values are not well established. Conformation effects on resonance interactions are discussed.