Electrons spread across several atoms, as in benzene, lowering energy and adding stability.
Practise Bonding & Molecular Structure All Bonding & Molecular Structure topics
Delocalization describes electrons that are shared among more than two atoms rather than confined to a single bond. Electrons occupying orbitals that span several atoms have lower kinetic energy, because their wavefunction is spread over a larger region, and this stabilizes the molecule. Delocalization occurs in conjugated systems with alternating single and double bonds, in resonance structures, in metals and in the band structure of solids. It explains the stability and reactivity of many organic molecules. The energy gained by delocalization is often called delocalization energy.
Key ideas: Look for it where a p orbital is adjacent to a pi bond, a lone pair or a charge, as in allyl, carboxylate, amide and enolate. More delocalization lowers energy, shortens single bonds between double bonds, and shifts absorption to longer wavelengths. Rule of thumb: the longer the conjugated chain, the smaller the HOMO-LUMO gap, so that beta-carotene with 11 conjugated double bonds is orange.
Common mistakes and connections: Students think delocalization requires alternating single and double bonds only, but lone pairs participate also. Another error is claiming that all adjacent double bonds are conjugated, as cumulated systems like allenes are not. Planarity is required for overlap. Links to resonance, aromaticity, dye colour and amide planarity.
The pi electrons of ozone are spread over all three oxygen atoms, a four-electron three-centre system that makes both O-O bonds equal in length. The interactive lesson shows this as a live animation or chart.
The four pi electrons in butadiene are spread over all four carbon atoms rather than localized in two separate double bonds.
Electrons spread across several atoms, as in benzene, lowering energy and adding stability.
Delocalization is a intermediate topic in Bonding & Molecular Structure. It builds on the vocabulary of beginner topics in this area.
Study these earlier topics in Bonding & Molecular Structure first: Diamagnetism, Paramagnetism, Heteronuclear Diatomic MOs.
The next topics in Bonding & Molecular Structure are Benzene Bonding and Aromaticity and Huckel's Rule.
Yes. The interactive lesson includes a self-check question on Delocalization, and the Bonding & Molecular Structure quiz draws on every topic in this area.
Delocalization is topic 67 of 104 in Bonding & Molecular Structure.