Aliphatic hydrocarbons are hydrocarbons that possess the basic properties of aliphatic compounds. They are composed of only carbon and hydrogen elements and are named after their initial extraction from fats.
Core Characteristics and Classification
Structural Characteristics: Carbon atoms are arranged in straight chains, branched chains, or rings (alicyclic hydrocarbons). The carbon skeleton is chain-like or cyclic with properties similar to chain hydrocarbons, distinguishing them from aromatic hydrocarbons.
Common Classifications: Classified by the type of chemical bond between carbon atoms:
Alkanes (saturated aliphatic hydrocarbons): Contain only carbon-carbon single bonds, general formula:
C<sub>n</sub>H<sub>2n</sub> + 2C<sub>n</sub>H<sub>2n+2</sub>
Alkenes (unsaturated aliphatic hydrocarbons): Contain carbon-carbon double bonds, general formula:
C<sub>n</sub>H<sub>2n</sub>C<sub>n</sub>H<sub>2n</sub>
Alkynes (unsaturated aliphatic hydrocarbons): Contain carbon-carbon triple bonds, general formula:
C<sub>n</sub>H<sub>2n−</sub>2C<sub>n</sub>H<sub>2n−2</sub>
Physical Properties:
State varies with the number of carbon atoms: 1-4 carbon atoms are generally gaseous, 5-16 are liquid, and 17 and above are solid (except for neopentane, which is gaseous);
Density is less than water; Melting and boiling points gradually increase with the number of carbon atoms; in isomers, the more branched the chain, the lower the melting and boiling points.
Chemical Properties:
Alkanes: mainly undergo substitution reactions and high-temperature cracking reactions;
Alkenes/Alkynes: chemically reactive, capable of addition reactions, polymerization reactions, oxidation reactions, substitution reactions, etc., among which addition and polymerization are the most commonly used reactions in industry.
Sources and Uses:
Aliphatic hydrocarbons are mainly derived from petroleum, natural gas, and coal. C1-C5 low-carbon aliphatic hydrocarbons are the basic raw materials for petrochemicals. Ethylene, propylene, and C4/C5 conjugated olefins are the most widely used in industry.