There are two major kinds of electron delocalization which is a stabilizing interaction or phenomenon in organic chemistry. The more electron delocalization the better (the more products will be predictable). Conversely, electrons are localized or don’t share electron density with neighboring orbitals are unstable.
- The second major type is collectively known as “hyperconjugation“. For example, hyperconjugation is responsible for the stability order of carbocations. The more substituted the carbocation, the more sigma bond to p-orbital (σ→π) overlap exists. That’s why primary is not as good (stable) as secondary or tertiary.
- The first and most obvious kind of delocalization is resonance stabilization by conjugation. This is when electrons delocalize through more than 2 adjacent p-orbitals. In general, the more resonance structures one can draw, the more stable the compound is.
- One sub-type of hyperconjugation (“negative hyperconjugation”) is the overlap of a lone pair in a p-orbital with an adjacent anti-bonding sigma (“sigma star”) orbital (π→σ*). This is more commonly known as the anomeric effect.
Electron Delocalization is central to understanding the stability of compounds, intermediates, and explains analytic techniques like mass spectrometry and all reactions outcomes depend on the extent and type of electron delocalization under discussion.