Nomenclature of Branched Alkanes

1.   Identify and name the parent chain.

• The parent chain is the longest consecutive chain of carbon atoms in the molecule.

2.   Identify and name all branches off the parent chain as alkyl groups.

• An alkyl group is an alkane that has had one H atom removed.
• If the H atom is removed from the end carbon of a straight-chain alkane, the alkyl group is named by changing the –ane suffix of the alkane to –yl.
• The name(s) of the alkyl group(s) precedes the name of the parent chain.

3.   Locate and assign a number to the position of each branch off the parent chain.

• For a single branch off the parent chain:
  • Count in the direction that gives the lowest number.
  • Place the number in front of the name of the alkyl group, separating the number and name with a hyphen (Example: 3-methyl).
• For multiple branches off the parent chain:
  • Count in the direction that gives the lowest of number for any branch off the parent chain.
  • For branches of the same type:
    • Indicate the number of that type by using the Greek prefixes di-, tri-, tetra-, etc. in front of the name of the alkyl group.
    • Write the number of the position of each branch in ascending order, separating the numbers by commas.
    • Example: 2,3,3-trimethyl
  • For branches of different types:
    • The alkyl groups are named in alphabetical order, with a number indicating the position of each alkyl group off the parent chain.
    • Example: 3-ethyl-2-methylhexane.

4.   Additional Notes

• The name of an alkane has no spaces.
• Numbers are separated by commas. Numbers and letters are separated by hyphens.
• Whether branched or unbranched, alkanes always have a general formula of C_nH_2n+2 and cycloalkanes always have a general formula of C_nH_2n.