CH-Bindungsmomente und IR-Intensität von Benzol-Derivaten—III. CH-Valenzschwingungen para-disubstituierter Benzol-Derivate

To analyse the interaction between substituents and aromatic CH bonds the intensities of the CH_ar stretching vibrations of 32 para-disubstituted benzene derivatives have been measured. For three discernible groups of p-benzene derivatives resulted a correlation between intensities and the sum of inductive parameters of Hammett constants [σ_I(X) + σ_I(Y)]. It was possible to invert the polarity of the moments of the CH bonds by strong electron acceptors. Hence the assumption of a C⁺H⁻ polarity in undisturbed benzene could be confirmed.