CID 7843
C4H10
Butane
- C 4
- H 10
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- IUPAC name
- butane
- Molar mass
- 58.124(10) g/mol
- Atoms
- 14
- SMILES
- CCCC
- InChIKey
- IJDNQMDRQITEOD-UHFFFAOYSA-N
- PubChem CID
- 7843
Butane boils at −0.5 °C, just below the temperature at which water freezes, so on most days only pressure keeps it liquid. The US Energy Information Administration (EIA) counts it among the hydrocarbon gas liquids, compounds that are gases in open air and liquids once compressed. Butane is shipped that way, as a liquefied gas under its own vapour pressure, and cigarette lighters hold it too.
The name is a small code. In the naming of alkanes, the prefix but- stands for four carbons and the ending -ane for an alkane, a hydrocarbon with the general formula CnH2n+2. Four carbon atoms and ten hydrogen atoms give C4H10, with a molar mass of 58.12 g/mol, and the carbons form an unbranched chain. The same atoms can also be joined as a branched chain, isobutane (2-methylpropane), a structural isomer: a compound with an identical formula but a different arrangement. In the fuel trade, “butanes” covers both.
Structure and bonding
The readout counts 14 atoms and 13 single bonds: three C–C bonds link the carbons, and ten C–H bonds fill the rest. With Labels on, each end carbon shows three H symbols and each middle one two, the CH3CH2CH2CH3 pattern of the straight chain. In Ball-and-stick the backbone zig-zags rather than running straight, because each carbon holds its four bonds in a tetrahedral arrangement, about 109.5° apart on Chem1’s account. PubChem’s computed model measures each C–C–C angle at 111.5° and each C–C bond at 1.52 to 1.53 Å. Turned edge-on, the model shows all four carbons almost in one plane.
The drawing matches the real bonding: every bond is a single covalent bond, with no ring, double bond or charge. Each carbon is sp3 hybridised, its outer s and p orbitals mixed into four identical ones aimed at tetrahedral corners. Each C–C bond forms where two such orbitals on neighbouring carbons overlap. Stick view strips away the atom spheres and leaves the zig-zag easiest to follow. Space-filling shows a long, smooth outline of hydrogen. Between elongated molecules lying side by side, Chem1 notes, dispersion forces, weak attractions present between all molecules, act along the whole length where they touch.
Where it turns up
Butane comes out of the ground with natural gas, and Haz-Map, a US occupational health database, lists it as a component of both natural gas and liquefied petroleum gas (LPG). Natural gas processing supplied about 90 per cent of all US hydrocarbon gas liquids in 2022, on EIA’s figures.
Once separated, butane fills cigarette lighters and aerosol cans, where it works as the propellant. Food additive and cosmetic ingredient lists carry it in the same propellant role, and it also serves as a refrigerant and a household and industrial fuel. For bottled gas, propane leads in the northern United States. Butane, whose boiling and freezing points are considerably higher, is used more widely in the warmer southern states.
Butane has also been reported in plants. The LOTUS natural-products database reports butane in Calendula officinalis, Stemona tuberosa and the genus Fragaria.
Why it matters
Most normal butane never reaches a lighter. EIA reports that the bulk of it is blended into motor gasoline, especially during the cooler months. In 1975, gasoline blending took about 90 per cent of butane consumption, according to the Hazardous Substances Data Bank (HSDB). Refiners also rearrange normal butane into its branched isomer by isomerisation, because demand for isobutane exceeds supply.
Butane is a petrochemical feedstock as well. Cracked in petrochemical plants, it yields butadiene among other chemicals, and butadiene is a precursor to synthetic rubber, according to EIA. Maleic anhydride, ethylene, acetic acid and formic acid are also made from it, on HSDB’s list. In 1975 about 4 per cent of butane went to butadiene and about 3 per cent to ethylene.
EIA credits Dr. Walter Snelling, a US scientist, with discovering butane, together with propane, in gasoline in 1912; the liquefied gases, he learned, could be stored and moved in pressurised containers.
Properties
| Property | Value | Unit | Source |
|---|---|---|---|
| Molecular formula (Hill order) | C4H10 | ||
| Molar mass | 58.124(10) g/mol | g/mol | IUPAC/CIAAW 2024 |
| Carbon atoms | 4 | ||
| Hydrogen atoms | 10 | ||
| Bonds | 13 | ||
| PubChem molecular weight | 58.12 g/mol | g/mol | PubChem |
Safety
Butane is an extremely flammable gas kept as a liquid under pressure, and its GHS (Globally Harmonized System) classification carries the signal word Danger. The gas is heavier than air, so it spreads at floor level and gathers in low-lying spaces, lowering the oxygen there. Rapidly evaporating liquid can cause frostbite. The PubChem Laboratory Chemical Safety Summary and the n-butane Pocket Guide card from NIOSH, the US National Institute for Occupational Safety and Health, cover handling and workplace exposure.
Questions
Why is butane a liquid in a lighter but a gas when it comes out?
Pressure holds it liquid. Butane boils at −0.5 °C, below room temperature, and at ordinary pressure it is a gas. The US Energy Information Administration groups it with the hydrocarbon gas liquids, which stay gaseous at atmospheric pressure and turn liquid when compressed. Inside the sealed lighter the pressure of butane's own vapour keeps most of the fuel liquid; once the valve opens, the escaping butane expands back into gas.
What shape is a butane molecule?
A bent chain rather than one named shape. Four carbon atoms sit in a row with no single central atom, and no one VSEPR (valence shell electron-pair repulsion) shape word covers the whole molecule. Each carbon is tetrahedral, its four bonds about 109.5° apart on Chem1's figure, and the backbone bends at each of the two middle carbons. PubChem's computed model has 14 atoms, 13 single bonds and C–C–C angles of 111.5°.
What is the difference between butane and isobutane?
They share the formula C4H10 but join their atoms differently, which makes them structural isomers. Normal butane is the unbranched chain CH3CH2CH2CH3. Isobutane, also named 2-methylpropane, is (CH3)2CHCH3: three carbons attached to a middle one. Demand for isobutane exceeds supply, so, according to the US Energy Information Administration, some normal butane is converted into it by isomerisation.
Where does butane come from?
From natural gas processing and oil refining. The US Energy Information Administration places hydrocarbon gas liquids, butane among them, as gases in the geologic formations that contain natural gas. Processing plants recover them, and fractionation splits the mixture into separate purity products, normal butane and isobutane each sold on its own alongside ethane and propane. Oil refineries add more, from catalytic cracking and catalytic reforming, where the butane is recovered as a liquid from the gas stream.
Made of the same elements
- C4H10 Isobutane 14 atoms, 13 single bonds.
- C5H12 Pentane 17 atoms, 16 single bonds.
- C3H8 Propane 11 atoms, 10 single bonds.
- C4H6 1,3-Butadiene 10 atoms, 9 bonds.
- C6H12 Cyclohexane 18 atoms, 18 single bonds.
- C3H6 Propylene 9 atoms, 8 bonds.
- C7H8 Toluene 15 atoms, 15 bonds.
- C6H6 Benzene 12 atoms, 12 bonds.
All 18 compounds made of carbon and hydrogen
- C2H6 Ethane 8 atoms, 7 single bonds.
- C6H14 Hexane 20 atoms, 19 single bonds.
- C8H8 Styrene 16 atoms, 16 bonds.
- C2H4 Ethylene 6 atoms, 5 bonds.
- C10H8 Naphthalene 18 atoms, 19 bonds.
- CH4 Methane 5 atoms, 4 single bonds, tetrahedral.
- C2H2 Acetylene 4 atoms, 3 bonds.
- C8H18 Isooctane 26 atoms, 25 single bonds.
- C10H16 Limonene 26 atoms, 26 bonds.
- C8H18 Octane 26 atoms, 25 single bonds.
Appears in these articles
- Why water is bent and carbon dioxide is straight: the VSEPR model Water's two bonds meet at 104.5°; carbon dioxide's lie in a straight line.
Sources
- PubChem CID 7843, butane
- IUPAC/CIAAW, Abridged Standard Atomic Weights 2024
- PubChem Laboratory Chemical Safety Summary for butane (CID 7843)
- NIOSH Pocket Guide to Chemical Hazards, n-Butane
- Stephen Lower, Chem1 General Chemistry, §9.5 Molecular Geometry (LibreTexts, CC BY 3.0)
- Stephen Lower, Chem1 General Chemistry, §9.6 The Hybrid Orbital Model (LibreTexts, CC BY 3.0)
- Stephen Lower, Chem1 General Chemistry, §7.2 Intermolecular Interactions (LibreTexts, CC BY 3.0)
- Stephen Lower, Chem1 General Chemistry, §4.5 Introduction to Chemical Nomenclature (LibreTexts, CC BY 3.0)
- US Energy Information Administration, Hydrocarbon Gas Liquids Explained
- US Energy Information Administration, Uses of hydrocarbon gas liquids
- US Energy Information Administration, Where do hydrocarbon gas liquids come from?