Lecture Notes: Understanding IUPAC Nomenclature in Chemistry

Introduction to IUPAC

• IUPAC: International Union of Pure and Applied Chemists
• Often perceived as making chemistry more difficult
• Aims to create a systematic and universal naming system for chemical compounds

Importance of IUPAC Naming

• Provides a universally understandable language for chemists
• Eliminates confusion in chemical nomenclature
• Allows chemists to deduce chemical structures from names

Basic Steps in Naming Organic Compounds

1. Determine the Longest Carbon Chain:

   • Use prefixes based on the number of carbons
     • 5 carbons: 'pent-', 7 carbons: 'sept-', etc.
     • Example: 23-carbon chain = 'tricosa-'
   • Find the longest carbon chain (e.g., hexane vs. pentane with ethane)

2. Identify the Suffix:

   • Depends on the presence of double or triple bonds
     • No multiple bonds: 'ane', one double bond: 'ene', one triple bond: 'yne'
   • Functional groups determine suffixes
     • Alcohols: '-ol' (e.g., methanol)
     • Aldehydes: '-al' (e.g., ethanal)
     • Ketones: '-one' (e.g., hexanone)
     • Amines: '-amine' (e.g., ethanamine)
     • Carboxylic Acids: '-oic acid' (e.g., ethanoic acid)

3. Precedence of Functional Groups:

   • Carboxylic acid has the highest precedence
   • Determines which functional group defines the suffix

4. Identify Side Chains and Additional Functional Groups:

   • Identify and number additional groups and double bonds
   • Use numbers to indicate positions (e.g., 3-methylbut-2-enoic acid)

Practical Example: Naming Angelic Acid

• Angelic Acid is a butene derivative due to a double bond
• With a methyl group, named as: 2-methylbut-2-enoic acid
• Correct numbering places carboxylic acid on carbon 1
• Identify the double bond as cis or trans

Building Chemical Structures from Names

• Example: Cinnamaldehyde (trans 3-phenylprop-2-enal)
  • Start with a three-carbon chain (prop)
  • Identify double bond location and phenyl group position
  • Place aldehyde on carbon 1

Conclusion

• IUPAC provides a systematic method to name organic compounds
• It's essential to understand prefix/suffix rules and functional group precedence
• Naming helps deduce chemical structure and ensures clarity

Episode Credits

• Written by Hank Green
• Chemistry consultant: Dr. Heiko Langner
• Filmed, edited, and directed by Nicholas Jenkins
• Additional contributors: Blake de Pastino, Caitlin Hofmeister, Michael Aranda, Thought Cafe