Complete Substituent Names

Step 3 of Branched-Alkane Nomenclature

Identify and number the substituents attached to the parent chain.

Substituent Locant

The number indicating the carbon atom of the parent chain to which a substituent is attached.

How is the location of a substituent specified?

Assign the substituent the number of the parent-chain carbon to which it is attached.

What if two substituents are attached to the same parent-chain carbon?

Give both substituents the same locant.

Number of Locants Required

There must be as many substituent locants in the complete name as there are substituents being specified.

Repeated Substituents

If two or more identical substituents occur, use a multiplicative prefix such as di-, tri-, or tetra- and include a locant for each substituent.

di-

A multiplicative prefix indicating two identical substituents.

tri-

A multiplicative prefix indicating three identical substituents.

tetra-

A multiplicative prefix indicating four identical substituents.

Step 4 of Branched-Alkane Nomenclature

Assemble the substituent locants and names with the parent hydrocarbon to form the complete compound name.

Alphabetical Ordering of Different Substituents

List different substituent names in alphabetical order in the complete IUPAC name.

Do di-, tri-, and tetra- count when alphabetizing substituents?

No. Multiplicative prefixes such as di-, tri-, and tetra- are ignored when determining alphabetical order.

Hyphens in an IUPAC Name

Use hyphens between numbers and words.

Commas in an IUPAC Name

Use commas between consecutive numbers.

Spaces in an IUPAC Alkane Name

Do not put spaces within the complete IUPAC name.

3-Methylhexane

A six-carbon parent chain with a methyl substituent attached to carbon 3.

3-Ethyl-4,7-dimethylnonane

A nine-carbon parent chain with an ethyl substituent at C3 and methyl substituents at C4 and C7.

3-Ethyl-2-methylhexane

A six-carbon parent chain with an ethyl substituent at C3 and a methyl substituent at C2; ethyl is cited before methyl alphabetically.

4-Ethyl-3-methylheptane

A seven-carbon parent chain with an ethyl substituent at C4 and a methyl substituent at C3.

4-Ethyl-2,4-dimethylhexane

A six-carbon parent chain with an ethyl substituent at C4 and methyl substituents at C2 and C4.

2,6-Dimethyloctane

An eight-carbon parent chain with methyl substituents attached at carbons 2 and 6.

Complete Branched-Alkane Naming Sequence

Choose the parent chain → number it → identify and locate substituents → alphabetize different substituents → assemble the complete name.