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3.3 Naming Alkenes and Alkynes

Lesson Summary

Naming Alkenes

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.

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:

Naming Alkynes

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