--- title: "Hybridisation, conjugation and delocalisation in organic molecules" description: "Organic structure has been drawn with lines that all look alike. Orbital mixing sets geometry. When p orbitals line up, electrons can be shared over several atoms, affecting bond length, strength and " canonical: https://lightmysky.com/learn/science/hybridisation-conjugation-and-delocalisation-in-organic-molecules-mt_Anv0MSQ4hq source: https://lightmysky.com/learn/science/hybridisation-conjugation-and-delocalisation-in-organic-molecules-mt_Anv0MSQ4hq.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Hybridisation, conjugation and delocalisation in organic molecules Organic structure has been drawn with lines that all look alike. Orbital mixing sets geometry. When p orbitals line up, electrons can be shared over several atoms, affecting bond length, strength and reactivity. Subject: Science · Area: Chemistry · Ages 18 to 19 Page: https://lightmysky.com/learn/science/hybridisation-conjugation-and-delocalisation-in-organic-molecules-mt_Anv0MSQ4hq ## Ready when they can - Assigns sp2 hybridisation to ethene carbon from stated sigma-bond and lone-pair counts, and relates sp3 and sp carbon models to ideal tetrahedral angles and linear geometry - Explains why neighbouring p-orbital alignment favours coplanarity in a conjugated region and why delocalisation restricts amide C-N rotation - Ranks otherwise comparable anion contributors with full octets and equal charge separation by negative-charge location, and rejects a contributor that moves a nucleus - Uses delocalisation to explain a measured bond length that lies between single and double ## Lesson: Hybrids set shape, sharing sets character Hybridisation is a local bonding model. Combining one s orbital with three p orbitals gives four sp3 hybrids; two p orbitals give three sp2 hybrids; one p orbital gives two sp hybrids. Their ideal geometries are tetrahedral (109.5 degrees), trigonal planar (120 degrees) and linear (180 degrees). The sp2 model leaves one unhybridised p orbital; the sp model leaves two. Without conjugation, count sigma bonds and local lone pairs: four suggests sp3, three sp2, two sp. A double bond contains one sigma and one pi bond; a triple bond has one sigma and two pi bonds. Each counts once in the sigma count. Alcohol oxygen has two sigma bonds and two lone pairs, so is usually sp3. Amine nitrogen is usually sp3 with three sigma bonds and one local lone pair. Conjugating lone pairs need a separate check. *(drawing: Check conjugation before using the count to assign hybridisation. These boxes show a method, not molecular geometry.)* Conjugation needs continuous overlap between neighbouring p orbitals. Alternating bonds, suitable lone pairs or empty p orbitals can take part. Coplanarity often improves overlap. Twisting reduces it without breaking a sigma bond; the whole molecule need not be flat. Resonance contributors keep nuclei, electron count and total charge fixed. They describe one electronic structure. The molecule does not switch between contributors. For common C, N and O anions, compare valid octets, then charge separation. With these comparable, negative charge on oxygen usually gives a larger contribution than on carbon. **Example.** An amide nitrogen's lone pair occupies a p orbital overlapping with the carbonyl. Its three sigma bonds use roughly planar sp2 hybrids. Carbonyl carbon and oxygen are also described as sp2. Partial C-N double-bond character makes twisting cost energy, so rotation is restricted. Carboxylate ions have two equivalent C-O bonds, intermediate in length between comparable single and double bonds. Delocalisation gives both partial double-bond character. Intermediate lengths support this model, but length alone is not proof. The value need not be exactly halfway. **Recap.** Check sigma bonds, lone pairs and conjugation before assigning hybrids. Delocalisation can change bond lengths and restrict rotation. *Lesson, questions and flashcards written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Benzene: Delocalisation and Electrophilic Substitution](https://lightmysky.com/learn/science/benzene-delocalisation-and-electrophilic-substitution-mt_jFqF7cZ0Ij) - [Naming Organic Compounds and the Formulas That Show Structure](https://lightmysky.com/learn/science/naming-organic-compounds-and-the-formulas-that-show-structure-mt_LCqg41gslT) - [Orbitals, Sub-Shells and Electron Configuration](https://lightmysky.com/learn/science/orbitals-sub-shells-and-electron-configuration-mt_sRMo1f5PfJ) ## Opens up - [Curly arrows as the language of mechanism](https://lightmysky.com/learn/science/curly-arrows-as-the-language-of-mechanism-mt_C0bq2Mu8HT) - [Pericyclic Reactions: The Diels-Alder and Orbital Symmetry](https://lightmysky.com/learn/science/pericyclic-reactions-the-diels-alder-and-orbital-symmetry-mt_I4i9d6aDgD) - [Molecular Symmetry: Elements, Operations and Point Groups](https://lightmysky.com/learn/science/molecular-symmetry-elements-operations-and-point-groups-mt_KcofGO11tm) - [Conformation: Newman Projections and the Chair](https://lightmysky.com/learn/science/conformation-newman-projections-and-the-chair-mt_N0_QpGF7Av)