Alkane Nomenclature

Introduction To Organic Compounds

Lecture Notes on Alkane Nomenclature

Systematic IUPAC Nomenclature of Unbranched Alkanes

Systematic IUPAC Nomenclature of Branched Alkanes

3-methylhexane

Naming the Isomers of C₇H₁₆

When there are two or more different types of alkyl groups branching off the main chain, locate them each by number and list them alphabetically.

When the same branching group appears more than once in a structure, the number times the group appears is indicated by a prefix:

Prefix	Number	Example
di	2	dimethyl
tri	3	trimethyl
tetra	4	tetramethyl
penta	5	pentamethyl
hexa	6	hexamethyl

The position of each group is listed separately by a locant number. The locant numbers are separated from each other by commas. The prefixes are disregarded in alphabetizing.

In complicated structures the "first point of difference" rule is useful in determining the proper way to number the parent chain.

When numbering this molecule the first branch occurs at position 2 from either direction. In numbering from the right, the second branch is also located at position 2. Numbering from the left, the second group would be at position 3. This is the first point of difference, and the group is given the lower number.

This molecule is numbered from right to left.

Non-alkyl Groups:

Group Name

F fluoro

Cl chloro

Br bromo

I iodo

NO₂ nitro

NH₂ amino

For cycloalkanes, the prefix cyclo- is added to the name of the corresponding open chain alkane.

Substituent positions are indicated by a number. Always begin numbering from a carbon bearing a substituent. Number around the ring giving the substituents the lowest possible numbers.