Resonance and mesomeric effects in molecules determine the exact chemical structure of the molecule. Resonance is the effect that describes the polarity of a molecule that is induced by interaction between lone electron pairs and bond electron pairs. Mesomeric effect is the effect of substituents or functional groups on chemical compounds. The main difference between resonance and mesomeric effect is that resonance occurs due to the interaction between lone electron pairs and bond electron pairs whereas mesomeric effect occurs due to the presence of substituent groups or functional groups.
