Lecture on IUPAC Naming of Organic Compounds

Introduction

• Importance of IUPAC naming in exams.
• Aim: Make IUPAC naming easy.
• Tips and tricks for writing IUPAC names.

Basic Steps for IUPAC Naming

1. Find the Longest Continuous Carbon Chain
   • Number the chain forward and backward.
   • Choosing the correct numbering for dealing with additional groups will be discussed later.
2. Determine the Root Name Based on Carbon Count
   • 1 C: meth-
   • 2 C: eth-
   • 3 C: prop-
   • 4 C: but-
   • 5 C: pent-
3. Identify Types of Bonds Between Carbon Atoms
   • Single bond: alkane (-ane)
   • Double bond: alkene (-ene)
   • Triple bond: alkyne (-yne)

Examples

Example 1

• Compound: Ethane
  • Two carbons.
  • Single bond (alkane).
  • IUPAC name: Ethane.

Example 2

• Compound: Propene
  • Three carbons.
  • Double bond between two carbons (alkene).
  • IUPAC name: Propene.

Example 3

• Compound: 2-Methylbutane
  • Longest chain: 4 carbons (but-).
  • Single bonds (alkane).
  • Methyl group on the second carbon.
  • IUPAC name: 2-Methylbutane.

Example 4

• Compound: 2,3-Dimethylbutane
  • Longest chain: 4 carbons (but-).
  • Single bonds (alkane).
  • Methyl groups on second and third carbons.
  • IUPAC name: 2,3-Dimethylbutane.

Example 5

• Compound: Chloropentane
  • Longest chain: 5 carbons (pent-).
  • Single bonds (alkane).
  • Chlorine substituent (chloro-).
  • IUPAC name: Chloropentane.

Example 6

• Compound: 3-Bromo-1,2-Dichloropentane
  • Longest chain: 5 carbons (pent-).
  • Single bonds (alkane).
  • Bromine on the third carbon, chlorine on the first and second carbons.
  • Alphabetical order of substituents.
  • IUPAC name: 3-Bromo-1,2-Dichloropentane.

Special Cases

Cyclic Compounds

• Cyclopentane: Cyclic structure with 5 carbons.
• Prefix: cyclo-
• IUPAC name: Cyclopentane.

Compounds with Double and Triple Bonds

• But-2-ene: 4 carbons (but-), double bond between second and third carbons.
  • IUPAC name: But-2-ene.
• Pent-1,3-diyne: 5 carbons (pent-), triple bonds starting at the first and third carbons.
  • IUPAC name: Pent-1,3-diyne.

Alcohols

• Butan-2-ol: Longest chain: 4 carbons (but-).
  • Alcohol (OH group): suffix -ol.
  • Position 2.
  • IUPAC name: Butan-2-ol.

Aldehydes and Ketones

• Pentanal: Including the aldehyde group carbon.
  • Prefix is based on the longest chain (pent-).
  • Suffix for aldehyde (-al).
  • Use the smallest possible number for position.
• Propanone (Acetone): 3 carbons (prop-), ketone group on the second carbon. Position usually not displayed for acetone.
  • IUPAC name: Propanone.

Carboxylic Acids

• Pentanoic acid: Longest chain: 5 carbons (pent-).
  • Carboxyl group (COOH).
  • Suffix -oic acid.
  • IUPAC name: Pentanoic acid.

Priority Order of Functional Groups

1. Carboxylic acids (COOH)
2. Aldehydes (CHO)
3. Ketones (C=O)
4. Alcohols (OH)
5. Triple bonds
6. Double bonds
7. Halogens (e.g., chloro-, bromo-)
8. Alkyl groups (e.g., methyl-, ethyl-)
   • Functional groups at higher priority affect suffix of the name, lower priority appear as prefixes.

Summary and Final Steps

• Always find the longest chain of carbons.
• Number the chain forward and backward.
• Identify functional groups and apply prefix/suffix.
• Follow the priority list for functional groups.
• Provide position numbers using the smallest possible values.
• Practice and apply these rules to get better at IUPAC naming.

Action Items

• Try the quiz linked below the video.
• Top three questions on this topic are available on the website.