Return to Contents
Basic IUPAC Organic Nomenclature

Simple Branched Alkanes

Simple branched alkanes are really alkanes with alkyl substituents.  The principles covered here will apply to other substituted systems in general.

The substituent is named in a similar way to the parent alkane. It is named based on the number of carbon atoms in the branch plus the suffix -yl.  

CH3-
methyl
CH3CH2- ethyl
CH3CH2CH2- propyl
CH3CH2CH2CH2- butyl
CH3CH2CH2CH2CH2- pentyl

In general an alkane type substituent becomes an alkyl group (often represented as "R-")

The name is then constructed in the standard way with locant + substituent prefix + root name  based on the basic rules.
When constructing the name, hyphens separate locants and letters, commas separate locants. No spaces.

Consider the following examples:

  • Functional group is an alkane, therefore suffix = -ane
  • The longest continuous chain is C5 therefore root = pent
  • The branch is a C1 alkyl group i.e. a methyl group
  • The first point of difference rule requires numbering from the right as drawn, the substituent locant is 2-
2-methylpentane
  

subs. alkane

CH3CH2CH2CH(CH3)2 
  • Functional group is an alkane, therefore suffix = -ane
  • The longest continuous chain is C5 therefore root = pent
  • The branch is a C2 alkyl group i.e. a ethyl group
  • The substituent locant is 3-
3-ethylpentane

subs. alkane
CH3CH2CH(CH2CH3)CH2CH3
  • Functional group is an alkane, therefore suffix = -ane
  • The longest continuous chain is C6 therefore root = hex
  • There are two substitutents, both C1 alkyl group i.e.  methyl groups
  • The first point of difference rule requires numbering from the left as drawn, the substituent locants are 3-  and 3-
3,3-dimethylhexane
 subs alkane
CH3CH2C(CH3)2CH2CH2CH3
  • Functional group is an alkane, therefore suffix = -ane
  • The longest continuous chain is C6 therefore root = hex
  • There are two substitutents, both C1 alkyl group i.e.  methyl groups
  • The first point of difference rule requires numbering from the left as drawn, the substituent locants are 2-  and 3-
2,3-dimethylhexane

subs alkane

(CH3)2CHCH(CH3)CH2CH2CH3
  • Functional group is an alkane, therefore suffix = -ane
  • The longest continuous chain is C6 therefore root = hex
  • One C1 alkyl group substituent i.e. a methyl group
  • One C2 alkyl group substituent i.e. an ethyl group
  • The first point of difference rule requires numbering from the right as drawn, the substituent locants are 2-  and 4-
 4-ethyl-2-methylhexane

subs alkane

(CH3CH2)2CHCH2CH(CH3)2

organic chemistry ©Dr. Ian Hunt, Department of Chemistry University of Calgary