Naming Hydrocarbons: Alkanes, Alkenes, and Alkynes

Introduction to Hydrocarbons

• Hydrocarbons can be classified into three main families:
  • Alkanes: Single bonds only.
  • Alkenes: At least one double bond between carbon atoms.
  • Alkynes: At least one triple bond between carbon atoms.

Importance of Naming Hydrocarbons

• Essential to have a systematic way to name hydrocarbons due to their vast number.
• Hydrocarbons are named based on two parts:
  1. Root Word: Indicates the number of carbon atoms.
  2. Suffix: Indicates the type of hydrocarbon (alkane, alkene, or alkyne).

Root Words for Carbon Atoms

• The root word denotes the number of carbon atoms:
  • 1 Carbon: meth
  • 2 Carbons: eth
  • 3 Carbons: prop
  • 4 Carbons: but
  • 5 Carbons: pent
  • 6 Carbons: hex
  • 7 Carbons: hept
  • 8 Carbons: oct
  • 9 Carbons: non
  • 10 Carbons: dec

Example of Root Words

• For a molecule with three carbons: prop
• For a molecule with one carbon: meth
• For a molecule with two carbons: eth

Suffixes for Hydrocarbon Types

• The suffix indicates the type of hydrocarbon:
  • Alkanes (single bonds): Suffix -ane
  • Alkenes (at least one double bond): Suffix -ene
  • Alkynes (at least one triple bond): Suffix -yne

Examples

• Propene: 3 Carbons, 1 Double Bond
• Methane: 1 Carbon, Alkane
• Ethylene: 2 Carbons, 1 Double Bond
• Ethyne: 2 Carbons, 1 Triple Bond

Naming from Molecular Formula

• Given a molecular formula (e.g., C4H8):
  1. Identify the root word based on carbon count.
  2. Determine the suffix using general molecular formulas:
     • Alkanes: CnH2n+2
     • Alkenes: CnH2n
     • Alkynes: CnH2n-2
• Example: C4H8
  • Root word: but
  • Hydrogen count indicates it’s an alkene (2x4=8), thus it’s butene.

More Examples

• C6H14

  • Root word: hex (6 Carbons)
  • Hydrogen count (14) = 2 more than double the Carbons (12), thus it’s an alkane: hexane.

• C9H16

  • Root word: non (9 Carbons)
  • Hydrogen count (16) = 2 less than double the Carbons (18), thus it’s an alkyne: nonyne.

Conclusion

• To name hydrocarbons, combine the root word for carbon count with the suffix based on bond type.
• For structures, check bonds; for formulas, use general formulas to determine suffixes.