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How are hydrocarbons classified and named systematically?

Classify hydrocarbons as alkanes, alkenes and alkynes, and apply IUPAC nomenclature to name straight-chain and branched compounds.

How to classify alkanes, alkenes and alkynes and apply IUPAC nomenclature rules - parent chain, locants, suffixes and substituent prefixes - to name straight-chain and branched hydrocarbons.

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  1. What this dot point is asking
  2. The three families
  3. The carbon-number stems
  4. IUPAC naming rules
  5. Worked names

What this dot point is asking

You must classify a hydrocarbon and give its systematic IUPAC name, including locants and substituents.

The three families

Family Bonding General formula Suffix
Alkane single bonds only CnH2n+2\text{C}_n\text{H}_{2n+2} -ane
Alkene one C=C double bond CnH2n\text{C}_n\text{H}_{2n} -ene
Alkyne one C≡C triple bond CnH2n−2\text{C}_n\text{H}_{2n-2} -yne

The carbon-number stems

The number of carbons in the parent chain sets the stem: meth- (1), eth- (2), prop- (3), but- (4), pent- (5), hex- (6), hept- (7), oct- (8). So a three-carbon alkane is propane, a three-carbon alkene is propene.

IUPAC naming rules

  1. Find the longest continuous carbon chain containing the multiple bond - this is the parent chain.
  2. Number the chain from the end that gives the multiple bond (or, for alkanes, the first branch) the lowest locant.
  3. Name the parent with the correct suffix, placing the locant of a double or triple bond just before the suffix (e.g. but-2-ene).
  4. Name branches (substituents) as alkyl groups (methyl, ethyl…) with their locants, listed alphabetically.
  5. Use di-, tri-, tetra- for repeated identical branches; separate numbers with commas and numbers from letters with hyphens.

Worked names

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