on benzaldehyde ring ortho to the imine group) were analysed by the Hammett single parameter and Tart dual substituent parameter (DSP) techniques. In the neutral solvent DMSO-d,, there is transmission of the electronic effects of substituents on the benzaldehyde ring to the H-a and H-2' protons, but no electronic transmission for substituents on the aniline ring. There is a dramatic change in acid media. Protonation of the imine group results in significant electronic transmission from substituents on the aniline ring to the H-a and H-2' protons, as well as an enhancement in electronic transmission from substituents on the benzaldehyde ring. DSP analysis indicates that both inductive and resonance factors are responsible for the observed electronic transmission effects, with resonance being the major factor.