Main Page | See live article | Alphabetical index Mesomeric effect attributed to a substituent in chemical compounds due to overlap of its p- or pi-orbitals with the p- or pi-orbitals of the rest of the molecular entity. The effect is symbolized by M. It occurs in unsaturated organic compounds, where the double bond is separated by a single bond. Examples butadi-1,3-ene, aromatic compounds. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.