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IUPAC Naming Basics

Note: This is a learning resource and may simplify some concepts for educational purposes.
Scope: This page covers basic alkane naming. Functional groups (like alcohols) follow additional priority rules.

The 4-Step Decision Flow

  1. Identify the Longest Carbon Chain (Parent Chain)

    Count the carbons in the longest continuous chain. This gives the base name (e.g., Propane, Butane, Octane).

  2. Identify the Highest Priority Group

    If there's a functional group (like -OH), it gets priority over simple branches.

  3. Number the Chain

    Number starting from the end that gives the priority group (or first branch) the lowest possible number (locant).

  4. Name the Substituents Alphabetically

    Ethyl comes before Methyl. If you have two methyls, use "dimethyl" (but alphabetize by "m").

Examples

2-methylpropane

Propane: 3-carbon chain.

2-methyl: A methyl group (CH3) attached to the 2nd carbon.

Tricky Case: Tie-Breaker

Scenario: Two chains have the same length?

Rule: Choose the chain that has more substituents (branches). This makes naming simpler.

1. The Basics: Counting Carbons

The base name of any organic molecule comes from the number of carbon atoms in the longest continuous chain.

Carbons Prefix Alkane Name
1 Meth- Methane
2 Eth- Ethane
3 Prop- Propane
4 But- Butane
5 Pent- Pentane
6 Hex- Hexane
7 Hept- Heptane
8 Oct- Octane
9 Non- Nonane
10 Dec- Decane

Multipliers (Branches)

If you have more than one of the same branch or group, use these prefixes before the branch name (e.g., dimethyl, triethyl).

  • 2: Di-
  • 3: Tri-
  • 4: Tetra-
  • 5: Penta-

2. Functional Groups Guide

Alkanes

Suffix: -ane

Rule: Single bonds only.

  • Example: Propane
  • Chain: 3 carbons
  • Structure: C-C-C

Alkenes

Suffix: -ene

Rule: Contains a Double Bond (=).

  • Example: Ethene
  • Chain: 2 carbons
  • Feature: Double Bond

Alkynes

Suffix: -yne

Rule: Contains a Triple Bond (≡).

  • Example: Ethyne
  • Chain: 2 carbons
  • Feature: Triple Bond

Alcohols

Suffix: -ol

Rule: Contains an -OH group.

  • Example: Ethanol
  • Chain: 2 carbons
  • Group: Hydroxyl (-OH)

Aldehydes

Suffix: -al

Rule: C=O at the end of the chain.

  • Example: Ethanal
  • Chain: 2 carbons
  • Group: C=O at end

Ketones

Suffix: -one

Rule: C=O in the middle of the chain.

  • Example: Propanone
  • Chain: 3 carbons
  • Group: C=O in middle

Carboxylic Acids

Suffix: -oic acid

Rule: Contains -COOH group at the end.

  • Example: Ethanoic acid
  • Chain: 2 carbons
  • Group: -COOH

Amines

Suffix: -amine

Rule: Contains Nitrogen (-NH2).

  • Example: Methanamine
  • Chain: 1 carbon
  • Group: -NH2

Haloalkanes

Structure: R—X (Where X represents the Halogen)

Prefix: Use the specific name for X:

  • X = F → Fluoro-
  • X = Cl → Chloro-
  • X = Br → Bromo-
  • X = I → Iodo-
  • Example: Chloroethane (where X = Cl)

Advanced Functional Group Naming

1. Haloalkanes

Position Matters

2-Bromopropane

  • Prefix: Bromo-
  • Position: Carbon 2
Multiple Groups

1,2-Dichloroethane

  • Multiplier: Dichloro
  • Positions: 1, 2

2. Alkenes

Position Matters

But-2-ene

  • Double Bond: Starts at Carbon 2
Multiple Groups

Buta-1,3-diene

  • Multiplier: diene
  • Positions: 1, 3

3. Alkynes

Position Matters

But-2-yne

  • Triple Bond: Starts at Carbon 2
Multiple Groups

Hexa-1,4-diyne

  • Multiplier: diyne
  • Positions: 1, 4

4. Alcohols

Position Matters

Hexan-3-ol

  • Group: -OH at Carbon 3
Multiple Groups

Butane-2,3-diol

  • Multiplier: diol
  • Positions: 2, 3

5. Ketones

Position Matters

Pentan-3-one

  • Group: C=O at Carbon 3
Multiple Groups

Pentane-2,4-dione

  • Multiplier: dione
  • Positions: 2, 4

6. Amines

Position Matters

Propan-2-amine

  • Group: -NH2 at Carbon 2
Multiple Groups

Ethane-1,2-diamine

  • Multiplier: diamine
  • Positions: 1, 2

7. Aldehydes

Always at End

Butanal

  • Position: Always Carbon 1
  • No number needed.
Multiple Groups

Pentanedial

  • Multiplier: dial
  • Two Carbonyls at ends.

8. Carboxylic Acids

Always at End

Propanoic Acid

  • Position: Always Carbon 1
  • No number needed.
Multiple Groups

Butanedioic Acid

  • Multiplier: dioic acid
  • Two Carboxyls at ends.

3. Naming Branches & Substituents

Most molecules aren't just straight lines. They have "branches" sticking off the main chain.

Step-by-Step Rules

  1. Find the Longest Chain: Count carbons. The longest continuous path is your base parent name (e.g., Hexane).
  2. Number the Chain: Start from the end closest to the first branch. You want branches to have the lowest possible numbers.
  3. Name & Order: Name the branches (e.g., Methyl, Ethyl). List them alphabetically (Ethyl before Methyl).

Example: 2-methylpentane

  • Longest Chain: 5 carbons → "Pentane"
  • Branch: 1 carbon group → "Methyl"
  • Position: At carbon #2 (counting from left)
  • Full Name: 2-methylpentane

Advanced Branching Rules

Multiple Groups of the Same Type

Use prefixes di-, tri-, tetra-. Each group needs its own number!

Two Branches (Di-)
  • 2,3-dimethylbutane
  • Parent: Butane (4C)
  • Branches: 2 Methyls at 2 & 3
Three Branches (Tri-)
  • 2,2,4-trimethylpentane
  • Parent: Pentane (5C)
  • Branches: 3 Methyls at 2, 2 & 4

Different Branches? Use Alphabetical Order!

When you have different types of branches (like Ethyl and Methyl), list them in Alphabetical Order.

  • Example: 3-ethyl-2-methylhexane
  • Ethyl: Starts with E (Listed First)
  • Methyl: Starts with M (Listed Second)
  • Note: Numbering still prioritizes the first branch encountered.

Time to Practice!

Next Topic Reading Structures →
Related Topic Common Reactions
Last updated: 2026-01-13

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