Lecture on Nomenclature of Alkanes: Cycloalkanes and Bicycloalkanes

Introduction to Cycloalkanes and Bicycloalkanes

• Discussed basic alkanes in ring structures (e.g., cyclohexane).
• Introduced concept of bicyclo compounds (bicycloalkanes) when two rings are present.
• Example: Two rings, one 6-membered and one 5-membered within a molecule.

Drawing Bicycloalkanes

• Example molecule drawn with seven carbons.
• Importance of drawing accurate rings with distinct gaps to avoid counting extra carbons.

Naming Bicycloalkanes

• Molecule with 7 carbons named bicycloheptane.
• Introduction to bridgehead carbons – the carbons joining the two rings.
• Example of identifying bridgehead carbons in a molecule.
• Explanation of how to distinguish between different bicyclo alkanes with the same number of carbons through bridgehead carbons.
• Example:
  • Identification of paths and carbons between bridgeheads.
  • Naming convention: Bicyclo[x.y.z]alkane format, where x, y, z are paths between bridgeheads.

Examples with Substituents

• Introduction of substituents (e.g., methyl) and how they impact naming.
• Example molecule named 8-methylbicyclo[3.2.1]octane.
• Another example molecule named 6-methylbicyclo[3.2.1]octane.
• Emphasis on giving substituents the lowest locant numbers.

Constitutional Isomers of Alkanes

• Definition: Same molecular formula, different connectivity.
• Examples:
  • Butane vs. isobutane drawn with the same molecular formula (C4H10).
  • Pentane and its constitutional isomers drawn and analyzed.
• The complexity increases with more carbons (e.g., C6H14, C7H16).
• Key challenge: Recognizing duplicates due to bond rotations.

Identifying Duplicates with Nomenclature

• Example of two structurally different-looking molecules being the same due to bond rotation.
• Importance of IUPAC naming to confirm duplicates.
• Visual challenges in identifying duplicates and use of model kits for understanding.

Combustion and Stability of Octanes

• Demonstrated combustion of octane producing CO2 and H2O, same for constitutional isomers of octane.
• Heat of combustion varies, indicating stability differences.
  • Linear octane: -5470 kJ/mol
  • Branched isomer: -5452 kJ/mol
• Stability illustrated via energy diagrams.
• More stable molecules release less heat upon combustion.
• Mention of calorimetry experiments to measure heat released/absorbed.

Summary

• Clear distinction of nomenclature for cycloalkanes and bicycloalkanes.
• Detailed explanation of identifying bridgehead carbons and paths within bicycloalkanes.
• Covered importance of proper naming to avoid duplications in constitutional isomers.
• Discussed combustion and stability of alkanes based on their structure.