Chemical Structure and Isomerism
Butane is a saturated hydrocarbon with the molecular formula C₄H₁₀. It belongs to the alkane family, characterized by single covalent bonds between carbon atoms. Butane exists in two structural isomers: n-butane (straight-chain) and isobutane (2-methylpropane, branched). The straight-chain structure of n-butane leads to higher intermolecular forces compared to the branched isobutane, which affects physical properties such as boiling point. The IUPAC name for n-butane is butane, while isobutane is 2-methylpropane. These isomers differ in stability, reactivity, and applications due to their distinct geometries.
Physical Properties
At standard temperature and pressure, butane is a colorless, odorless gas. Its physical properties are influenced by its molecular structure:
- Boiling point: -0.5°C for n-butane; -12°C for isobutane.
- Melting point: -138.3°C for n-butane; -159.6°C for isobutane.
- Density: Gas form has a density of ~2.48 kg/m³; liquid form (under pressure) is approximately 0.58 g/cm³.
- Solubility: Poorly soluble in water (~0.006 g/100 mL) but miscible with nonpolar solvents.
Both isomers can be liquefied under pressure, making them suitable for storage and transport as liquefied petroleum gas (LPG).
Chemical Properties and Reactions
As an alkane, butane is relatively inert but participates in combustion and substitution reactions. Key reactions include:
- Combustion: Burns in oxygen to produce carbon dioxide and water:
$$ 2C_4H_{10} + 13O_2 \rightarrow 8CO_2 + 10H_2O + \text{energy} $$ This exothermic reaction is exploited in