The ionisation potential of acetophenones p‐substituted by -NO₂ , -Cl, -H, -CH₃ , -OH, and -NH₂ , and the appearence potential of the methyl, acetyl, and phenyl‐substituted ions formed by cleavage of these ketones have been determined by mass spectrometry.

These potentials give very good linear correlations with the σ_p Hammett constants.

It is interesting to note that the inductive and mesomeric effects are regularly transmitted along a long conjugate chain for the separation of an electron from the ketone oxygen (ionisation potential) as well as for the displacement of an electron pair, as is the case in the formation, by a dative bond, of the adducts with the electronic acceptors.

The calculated correlations show that the electron-donor substituants lower the radial ionisation or appearance potentials of the ions formed by the cleavage of a neutral radical from the molecule, leaving the substituted phenyl residue attached to the positive ion ; the electron-acceptor substituants have an opposite effect.

On the contrary, the appearance potential of the positive acetyl ion is increased by electron-donor substituants and lowered by electron-acceptor substituants.