Skip to main content
Chemistry LibreTexts

Nomenclature of Alkanes II

I. The parent compound must have the longest chain of carbon atoms

Learn: methane (1 carbon atom), ethane (2 carbon atoms), propane (3 carbon atoms), butane (4 carbon atoms), pentane (5 carbon atoms), hexane (6 carbon atoms), heptane (7 carbon atoms), octane (8 carbon atoms), nonane (9 carbon atoms) and decane (10 carbon atoms).

Try to name the following compounds:

  1. CH3-CH2-CH2-CH3
  2. CH3-CH2-CH2-CH2-CH2-CH3
  3. CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

Try to draw structures for the following compounds:

  1. propane
  2. pentane
  3. octane

II. The parent chain is numbered to give substituents the lowest possible numbers

Substituent names are methyl, ethyl, propyl, butyl, etc. The number showing the point of attachment to the parent chain precedes the substituent name. If you have more than one substituent with the same name, a number of attachment must be given for each substituent and the number of the substituents must be designated with di-, tri-, etc.

Try to name the following compounds...

7.                                                                              

 

8.                                                                
 

 

9.                                                

Try to draw structures for the following compounds...

  1. 2,2-dimethylpropane
  2. 3-methylheptane
  3. 4,5-diethylnonane

III. Substituents are named in alphabetical order

Remember that the numbering of the parent chain must give all substituents the lowest possible numbers regardless of their names.

Try to name the following compound...

13.                                                    

IV. A large substituent is numbered to give its point of attachment

The point of attachment is number one and any other smaller groups are named as substituent groups on the larger group. This numbering is independent of the numbering of the parent chain. Try to name the following compounds...

14.

                                                 

  
15.                                      

 

Try to draw structures for the following compounds...

  1. 4-(1-methylethyl)heptane
  2. 5-(1,1-dimethylethyl)nonane

V. Ring compounds are designated with a cyclo- prefix and are numbered to give multiple substituents the lowest possible numbers

A single substituent does not need to be numbered. A ring can also be named as a substituent. Try to name the following compounds:

18.                                                 
 
 

19.                                                     
 
 

20.                                                         

 

Try to draw structures for the following compounds...

  1. ethylcyclobutane
  2. 1-ethyl-4-methylcyclohexane
  3. cyclobutylcyclooctane

VI. Common Names

  • isopropyl = 1-methylethyl
  • isobutyl = 2-methylpropyl
  • sec-butyl = 1-methylpropyl
  • tert-butyl = 1,1-dimethylethyl
  • neo-pentyl = 2,2-dimethylpropyl
  • iso-pentyl = 3-methylbutyl

Try to name the following compounds using common names...

24.

25.  
 
 

Try to draw structures for the following compounds...

  1. 4-isopropyloctane
  2. isopentylcyclohexane

Answers

  1. butane
  2. hexane
  3. nonane
  4. CH3-CH2-CH3
  5. CH3-CH2-CH2-CH2-CH3
  6. CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3
  7. 2-methylbutane
  8.  3-ethylhexane
  9. 3-methyloctane (Remember that you must number the parent chain to give the substituent the lowest possible number.)
  10. 4-ethyl-3-methylheptane
  11. 4-(1-methylethyl)octane

  12. 5-(1-methylpropyl)decane

  13. 1-ethyl-2-methylcyclohexane

  14. methylcyclopentane (You do not need a number since there is only one substituent and it is assumed to be on the first carbon regardless of how the ring compound is drawn.)

  15. cyclopropylcyclopentane

  16. neo-pentylcycloheptane (1-(2,2-dimethyl-1-propyl)cycloheptane is the proper name.)

  17. isopropylcyclohexane