Hydrocarbon
A hydrocarbon is an organic compound consisting entirely of hydrogen and carbon atoms, forming the simplest class of organic molecules. Hydrocarbons are classified by their bonding: saturated (single bonds only) or unsaturated (containing double or triple bonds). They are the primary constituents of fossil fuels and serve as feedstocks for the petrochemical industry.
Key Formula
Alkane: CnH(2n+2); Alkene: CnH(2n); Alkyne: CnH(2n-2)
LaTeX: C_nH_{2n+2} \text{ (alkane)}, \quad C_nH_{2n} \text{ (alkene)}, \quad C_nH_{2n-2} \text{ (alkyne)}
| Symbol | Meaning | Unit |
|---|---|---|
| n | number of carbon atoms in the chain | dimensionless |
Worked Example
Problem
An unknown hydrocarbon has molecular formula C₄H₆. Determine whether it is an alkane, alkene, or alkyne.
Solution
Step 1: For an alkane, C₄ requires H = 2(4)+2 = 10. But we have 6 H, not 10. Step 2: For an alkene, C₄ requires H = 2(4) = 8. We have 6 H, not 8. Step 3: For an alkyne, C₄ requires H = 2(4)−2 = 6. This matches! Step 4: The compound could also be a cycloalkene (diene). Since C₄H₆ fits CnH(2n-2), it is classified as an alkyne or diene.
Answer
C₄H₆ is an alkyne (e.g., 1-butyne) or a diene (e.g., 1,3-butadiene)
Classification of Common Hydrocarbons
| Class | General Formula | Bond Type | Example | Boiling Point (°C) |
|---|---|---|---|---|
| Alkane | CnH(2n+2) | C–C single | Methane (CH₄) | −161.5 |
| Alkene | CnH(2n) | C=C double | Ethylene (C₂H₄) | −104 |
| Alkyne | CnH(2n-2) | C≡C triple | Acetylene (C₂H₂) | −84 |
| Cycloalkane | CnH(2n) | C–C single (ring) | Cyclohexane | 80.7 |
| Aromatic | Variable | Delocalized π | Benzene (C₆H₆) | 80.1 |
Interactive Tools
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Related Terms
Alkane
An alkane is a saturated hydrocarbon in which all carbon atoms are connected by single covalent bonds, giving the general formula CₙH₂ⁿ₊₂. Because alkanes contain no double or triple bonds, they are chemically less reactive than other hydrocarbons and are described as "paraffins" in the petroleum industry. They are the principal components of natural gas and crude oil, making them critical energy sources.
Alkene
An alkene is an unsaturated hydrocarbon containing at least one carbon–carbon double bond (C=C), with the simplest members following the general formula CₙH₂ⁿ. The double bond consists of a sigma bond and a pi bond, making alkenes more reactive than alkanes and susceptible to addition reactions. Alkenes are industrially vital — ethylene alone is the most-produced organic chemical worldwide, used to make polyethylene plastic.
Alkyne
An alkyne is an unsaturated hydrocarbon that contains at least one carbon–carbon triple bond (C≡C), with the simplest acyclic alkynes following the general formula CₙH₂ⁿ₋₂. The triple bond comprises one sigma and two pi bonds, making alkynes highly reactive and capable of two successive addition reactions. The simplest alkyne, acetylene (ethyne), is widely used in welding torches because its combustion with oxygen produces a flame exceeding 3,500 °C.
From Greek "hydor" (water) and Latin "carbo" (coal/carbon). The term reflects the two elements: hydrogen and carbon. First systematically studied in the 19th century by chemists working with coal tar and natural gas.