Overview
This lecture explains the rules for naming bicyclic compounds in organic chemistry, covering bridged, fused, and spiro systems, including how to number and name substituents.
Types of Bicyclic Compounds
- Bicyclic compounds contain two rings within their structure.
- The three main types are bridged bicyclics, fused bicyclics, and spiro bicyclics.
Naming Bridged and Fused Bicyclic Compounds
- Identify the total number of carbons for the parent name (e.g., bicyclooctane for 8 carbons).
- Find the two bridgehead carbons, present in all rings.
- Count carbons between bridgeheads on all paths (do not count the bridgeheads themselves).
- Write these numbers in descending order inside brackets: [x.y.z].
- For fused bicyclics, one path directly connects bridgeheads (this count is zero).
- Number the ring by starting at a bridgehead, through the longest path first.
- Number substituents to give the lowest possible locator number.
Naming Spiro Bicyclic Compounds
- Spiro compounds share a single "spirocarbon" connecting two rings.
- Name starts with "spiro" instead of "bicyclo".
- Count the number of carbons in each ring (excluding the spirocarbon).
- Place the counts in ascending order inside brackets: [smaller.larger].
- For numbering, do not start with the spirocarbon; start on the smaller ring for lower numbers.
- Number to give substituents the lowest possible locator number.
Functional Group Priority in Nomenclature
- Only the highest-priority functional group is named as a suffix in the parent chain.
- Other functional groups are named as substituents (prefixes).
- Priority order (e.g., carboxylic acid > anhydride > ester, etc.) should be learned for applying correct suffixes and prefixes.
Key Terms & Definitions
- Bicyclic compound — a molecule containing two connected rings.
- Bridgehead carbons — carbons shared by both rings in a bridged or fused system.
- Spirocarbon — single carbon atom where two rings are joined in a spiro compound.
- Fused bicyclic — two rings sharing two adjacent carbons (directly bonded bridgeheads).
- Bridged bicyclic — two rings sharing two non-adjacent carbons (bridgeheads), separated by bridges of varying length.
Action Items / Next Steps
- Study the functional group priority list for nomenclature.
- Review and practice naming bicyclic structures with and without substituents.
- Prepare for upcoming lessons on conformational structures of alkanes.