Aliphatic hydrocarbons
Organic chemistry is the chemistry of carbon compounds. Carbon atoms form four bonds and can join to each other in chains and rings. A hydrocarbon contains only hydrogen and carbon. Aliphatic hydrocarbons have the carbons in chains (not in a benzene ring). They are the main part of crude oil and natural gas.
| Family | General formula | Bonds | First member |
|---|---|---|---|
| Alkanes | CₙH₂ₙ₊₂ | All single bonds (saturated) | Methane, CH₄ |
| Alkenes | CₙH₂ₙ | One C=C double bond (unsaturated) | Ethene, C₂H₄ |
| Alkynes | CₙH₂ₙ₋₂ | One C≡C triple bond (unsaturated) | Ethyne, C₂H₂ |
A homologous series is a family of compounds with the same general formula and the same functional group. Each member differs from the next by CH₂. Members have similar chemical properties and a gradual change in physical properties: the boiling point rises as the chain gets longer.
Alcohols
Alcohols contain the hydroxyl group (–OH). Their general formula is CₙH₂ₙ₊₁OH. Methanol is CH₃OH, ethanol is C₂H₅OH and propanol is C₃H₇OH. Ethanol is used as a fuel, solvent and in drinks and disinfectants.
IUPAC naming of C1 to C10 compounds
| Carbons | Stem | Alkane | Alkene | Alcohol |
|---|---|---|---|---|
| 1 | meth- | methane | — | methanol |
| 2 | eth- | ethane | ethene | ethanol |
| 3 | prop- | propane | propene | propan-1-ol |
| 4 | but- | butane | but-1-ene | butan-1-ol |
| 5 | pent- | pentane | pent-1-ene | pentan-1-ol |
| 6 | hex- | hexane | hex-1-ene | hexan-1-ol |
| 7 | hept- | heptane | hept-1-ene | heptan-1-ol |
| 8 | oct- | octane | oct-1-ene | octan-1-ol |
| 9 | non- | nonane | non-1-ene | nonan-1-ol |
| 10 | dec- | decane | dec-1-ene | decan-1-ol |
Isomers are compounds with the same molecular formula but different structures. Butane (C₄H₁₀) has two isomers: butane (a straight chain) and 2-methylpropane (branched). Pentane has three isomers.
Choose the number of carbon atoms in an alkane. Use the general formula CₙH₂ₙ₊₂. (C = 12, H = 1)
Key terms
- Hydrocarbon
- A compound of carbon and hydrogen only.
- Homologous series
- A family of compounds with the same functional group and general formula, each differing by CH₂.
- Isomers
- Compounds with the same molecular formula but different structures.
- Saturated
- Having only single bonds between carbon atoms.
Summary
- Alkanes CₙH₂ₙ₊₂ are saturated; alkenes CₙH₂ₙ and alkynes CₙH₂ₙ₋₂ are unsaturated.
- Alcohols contain –OH and have the formula CₙH₂ₙ₊₁OH.
- Stems: meth, eth, prop, but, pent, hex, hept, oct, non, dec.
- Isomers share a formula but have different structures.