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3.3 Naming Alkenes

Lesson Summary

When naming alkenes, the same rules apply for alkanes with the addition of four rules:

  • 1. Use suffix “-ene” instead of “-ane”.
  • 2. Add a number at the start of the double bond.
  • 3. Add prefixes “cis” or “trans” for alkenes with different priority substituents, and at least one hydrogen on either side of the alkene.
  • 4. If all substituents are different, use the E/Z naming system, where E = highest priority substituents on opposite sides, and Z = highest priority substituents on the same side.

  • 1. Use suffix “-yne” instead of “-ane”.
  • 2. Add a number at the start of the triple bond.

Determining priority

  • 1. Highest atomic number = highest priority.
  • 2. If there’s a tie, keep going to adjacent carbons until you break the tie.
  • 3. Multiple-bonded atoms are counted as the same number of single-bonded atoms: