Pielectron

Pielectron is not a widely used term in modern chemistry. The standard terminology is π electron (pi electron) or pi electrons, referring to electrons in pi bonds or in conjugated systems. The concept is central to understanding bonding and reactivity in organic chemistry.

Pi electrons arise from the sideways overlap of adjacent p orbitals on atoms participating in a double bond or a conjugated network. These electrons occupy pi molecular orbitals that can be localized between two atoms or delocalized over an extended framework, giving rise to conjugation and, in aromatic systems, exceptional stability.

Pi electrons influence many properties: bond strengths, reaction pathways, and the electronic spectra of molecules. In aromatic compounds, the π system obeys Hückel's rule, where planar, cyclic systems with 4n+2 π electrons are especially stable; non-aromatic or anti-aromatic systems have different stabilities.

Common examples include the six π electrons of benzene, two π electrons per carbon–carbon double bond in polyenes, and the extended delocalized π system in graphene and graphite.

Measurement and analysis of π electrons employ techniques such as UV–visible spectroscopy, which probes π to π* transitions, and computational methods based on molecular orbital theory.