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IUPAC Naming
Functional Group Compounds

Master the systematic approach to naming organic molecules with functional groups: alcohols, aldehydes, ketones, carboxylic acids, and more.

Organic Chemistry 1

What is IUPAC Naming?

IUPAC (International Union of Pure and Applied Chemistry) naming is the universal language for identifying organic compounds. Every chemist worldwide uses the same set of rules to assign a unique, unambiguous name to each molecule.

What are Functional Groups?

A functional group is a specific arrangement of atoms within a molecule that determines the compound's chemical reactivity and physical properties. The carbon backbone is just the skeleton: the functional group gives the molecule its personality.

\( \text{-OH} \)
Hydroxyl group: makes an alcohol
\( \text{-CHO} \)
Aldehyde group: always at the chain end
\( \text{-COOH} \)
Carboxyl group: a carboxylic acid
\( \text{C=O} \)
Carbonyl (mid-chain): a ketone

Why Does Naming Matter?

Common names like "acetone" or "formaldehyde" give you zero structural information. IUPAC names tell you exactly what the molecule looks like, which is essential for:

1
Communication: Scientists everywhere understand the same name without ambiguity.
2
Predicting properties: The name tells you the functional group, chain length, and branching.
3
Database searching: Chemical databases index compounds by their IUPAC names.

The Naming Blueprint

Substituent Prefix e.g. 3-methyl Parent Chain Root Word e.g. but-, pent- Functional Group Suffix e.g. -ol, -al, -one = IUPAC Name

Functional Group Priority

When a molecule has multiple functional groups, the one with the highest priority determines the suffix. Lower-priority groups become prefixes.

Priority Functional Group Suffix As Prefix
1 (Highest) Carboxylic acid -oic acid carboxy-
2 Aldehyde -al oxo-
3 Ketone -one oxo-
4 Alcohol -ol hydroxy-
5 Amine -amine amino-

Parent Chain Root Words

The root word tells you the number of carbons in the longest continuous chain that includes the principal functional group.

1C: meth-
Methane backbone
2C: eth-
Ethane backbone
3C: prop-
Propane backbone
4C: but-
Butane backbone
5C: pent-
Pentane backbone
6C: hex-
Hexane backbone

Suffix vs Prefix: Key Distinction

Suffix (Principal Group)
The highest-priority functional group in the molecule. It determines the ending of the name. Only one suffix per name. Example: an \( \text{-OH} \) group on pentane gives pentan-ol.
Prefix (Substituent)
Any lower-priority group or branch. Added to the front of the name with a locant number. Example: a methyl branch gives 3-methylpentanol. Multiple prefixes listed alphabetically.

Step-by-Step Naming Process

1
Identify the principal functional group. This determines your suffix (-ol, -al, -one, -oic acid, etc.).
2
Find the longest carbon chain that includes the principal functional group. This gives you the root word.
3
Number the chain so that the principal functional group gets the lowest possible locant.
4
Name all substituents (branches and lower-priority groups) as prefixes with their locant numbers.
5
Assemble the name: prefixes (alphabetical) + root + suffix. Include locants separated by hyphens.

Example 1: Naming an Alcohol

C1 C2 C3 C4
\(\text{OH}\)
 Functional group at C2 Root: but- (4 carbons) Suffix: -an-2-ol
Butan-2-ol

Example 2: Naming an Aldehyde

C1 C2 C3 O H
\(\text{-CHO}\) always at C1
 Root: prop- (3C) Suffix: -anal Propanal

Example 3: Naming a Ketone

C1 C2 C3 C4 C5 O
\(\text{C=O}\) at C3 (mid-chain)
 Root: pent- (5C) Suffix: -an-3-one Pentan-3-one

Example 4: Carboxylic Acid with a Branch

C1 C2 C3 C4 O
\(\text{OH}\)
\(\text{CH}_3\)
 methyl at C3 3-methylbutanoic acid prefix + root + suffix

Naming Amines

C1 C2 C3
\(\text{NH}_2\)
 Suffix: -amine Root: prop- (3C) Propan-2-amine

Common Mistakes to Avoid

✕ Wrong Chain Selection
Choosing the longest chain overall instead of the longest chain that includes the principal functional group.
✕ Highest Locant
Numbering the chain from the wrong end, giving the functional group a higher locant instead of the lowest possible.
✕ Wrong Priority
Using a lower-priority group as the suffix. Example: naming as an alcohol (-ol) when a ketone (-one) is also present.

Quick Reference Summary

Functional Group Formula Suffix Example
Carboxylic acid \(\text{-COOH}\) -oic acid Ethanoic acid
Aldehyde \(\text{-CHO}\) -al Propanal
Ketone \(\text{C=O}\) (internal) -one Pentan-3-one
Alcohol \(\text{-OH}\) -ol Butan-2-ol
Amine \(\text{-NH}_2\) -amine Propan-2-amine

Question 1 of 5

A 5-carbon chain with a hydroxyl group (\(\text{-OH}\)) on carbon 3 would be named:

Question 2 of 5

What suffix is used to name an aldehyde in IUPAC nomenclature?

Question 3 of 5

A molecule has both a \(\text{-COOH}\) group and an \(\text{-OH}\) group. Which group determines the suffix?

Question 4 of 5

The compound 3-methylbutanal has which structural features?

Question 5 of 5

When numbering the parent chain, the principal functional group should receive: