resonance effect

https://doi.org/10.1351/goldbook.08204
Experimentally observable influence (on reactivity, etc.) of a substituent through electron delocalization to or from the substituent.
Source:
PAC, 2022, 94, 353. (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 2021)) on page 499 [Terms] [Paper]