Using ab initio GIAO calculations the experimental ¹H NMR spectra of the E and Z isomers of alkyl phenyl ketone phenylhydrazones R1–C(Ph)N–NH–Ph (R1 = Me, Et, iPr, and tBu) have been re-interpreted and deviations from Karabatsos' rule or from the assignment of Bellamy and Hunter have been discussed in the light of the optimized geometrical structures.