--- title: "Naming Organic Compounds and the Formulas That Show Structure" description: "Every organic name is built from a stem for the longest chain, a suffix for the main functional group and prefixes for whatever hangs off it. Molecular, structural, displayed and skeletal formulas eac" canonical: https://lightmysky.com/learn/science/naming-organic-compounds-and-the-formulas-that-show-structure-mt_LCqg41gslT source: https://lightmysky.com/learn/science/naming-organic-compounds-and-the-formulas-that-show-structure-mt_LCqg41gslT.md retrieved: 2026-09-12 --- > **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`. # Naming Organic Compounds and the Formulas That Show Structure Every organic name is built from a stem for the longest chain, a suffix for the main functional group and prefixes for whatever hangs off it. Molecular, structural, displayed and skeletal formulas each show a different amount of that structure. Subject: Science · Area: Chemistry · Ages 16 to 17 Page: https://lightmysky.com/learn/science/naming-organic-compounds-and-the-formulas-that-show-structure-mt_LCqg41gslT ## Ready when they can - Names a branched alkane, an alcohol and a haloalkane with the locants as low as the rules allow - Converts between displayed, structural and skeletal formulas for the same molecule - Picks the functional group out of an unfamiliar molecule and names the family it belongs to - Explains what a homologous series is and what its general formula lets you predict ## Lesson: Naming organic molecules piece by piece Every organic name is built from three parts. Find the longest carbon chain for the stem: meth for 1, eth for 2, prop for 3, but for 4. Take the suffix from the main functional group: plain -e for alkanes and -ol for alcohols. Hang everything else off as prefixes with numbers, and list prefixes alphabetically. **Example.** CH3CH(CH3)CH2CH3 is 2-methylbutane: the longest chain has five carbons and the branch gets the lowest locant by numbering from the nearer end. CH3CH(OH)CH2CH3 is butan-2-ol: the hydroxyl group gets the lowest possible number and -ol replaces the -e ending. Never write butan-3-ol, because you always number to flatter the functional group. The same molecule can be drawn four ways. The molecular formula C4H10 just counts atoms. The structural formula CH3CH2CH2CH3 groups them. The displayed formula draws every bond and atom, which is slow but unambiguous. The skeletal formula draws zigzag lines where each kink and end is a carbon, the fastest once you can read it. To expand skeletal to displayed, put a carbon on every kink and end, then add hydrogens until each carbon has four bonds. Check your atom count at both ends. **Tip.** Spot the family before you name anything. A hydroxyl -OH marks an alcohol, a C-Cl or C-Br bond marks a haloalkane, and a C=O in the middle marks a ketone. The suffix and the numbering priority both follow from the family. Families stack into homologous series where each member adds one CH2 to the last: alkanes run CnH2n+2 and alcohols run CnH2n+1OH. Neighbours share reactions with gradually shifting properties, so the general formula predicts the next member before anyone makes it. **Recap.** A name is stem plus suffix plus prefixes, and the formula style you draw should fit the job. ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Covalent Bonding: Shared Pairs and Simple Molecules](https://lightmysky.com/learn/science/covalent-bonding-shared-pairs-and-simple-molecules-mt_fn5Dq6qUjP) - [Alkanes and Alkenes: The First Homologous Series](https://lightmysky.com/learn/science/alkanes-and-alkenes-the-first-homologous-series-mt_mkLJDtBanL) ## Opens up - [Hybridisation, Conjugation and Delocalisation in Organic Molecules](https://lightmysky.com/learn/science/hybridisation-conjugation-and-delocalisation-in-organic-molecules-mt_Anv0MSQ4hq) - [Isomerism: Same Formula, Different Molecule](https://lightmysky.com/learn/science/isomerism-same-formula-different-molecule-mt_DvD0coeKZe)