mesomérico

Mesomérico is a term used in chemistry to describe a specific type of electron delocalization. It refers to the effect where electrons in a pi system are drawn into or pushed out of a conjugated system by an adjacent atom or group possessing lone pairs or vacant p orbitals. This phenomenon is closely related to resonance. When a substituent has lone pairs of electrons that can participate in resonance with a pi system, it is said to exert a positive mesomeric effect (+M). This donation of electrons into the pi system increases electron density at specific positions. Conversely, if a substituent has a vacant p orbital that can accept electrons from a pi system, it exhibits a negative mesomeric effect (-M). This withdrawal of electrons from the pi system decreases electron density at specific positions. The mesomeric effect significantly influences the reactivity and electronic properties of molecules, particularly in aromatic compounds. It is a crucial concept for understanding electrophilic and nucleophilic aromatic substitution reactions, as well as the acidity and basicity of various organic functional groups. The extent of the mesomeric effect depends on the nature of the substituent and the conjugated system.