Hydrocarbon Nomenclature

  • construct models, identify the functional group, and write structural and molecular formulae for homologous series of organic chemical compounds, up to C8 (ACSCH035):
    • alkanes
    • alkenes
    • alkynes

 

 Naming Hydrocarbons (Nomenclature)

  • Nomenclature of organic carbons including hydrocarbons must account for:
    • Functional group(s) and their positions
    • Number of carbon atoms in the longest chain (stem)
    • Type and position of substituents

 

 

Number of carbon atoms in the longest chain

No. of Carbons

Name

Molecular formula

1

Methane

CH4

2

Ethane

C2H6

3

Propane

C3H8

4

Butane

C4H10

5

Pentane

C5H12

6

Hexane

C6H14

7

Heptane

C7H16

8

Octane

C8H18

Function group of hydrocarbons

Functional group

Suffix

Example

Alkane

-ane

Ethane

Alkene

-ene

Ethene

Alkyne

-yne

Ethyne

 

  • Alkanes and alkenes can have cyclo- compounds in which the longest carbon chain forms a ring. This unique type of hydrocarbon is specified by a prefix of ‘cyclo’ before its functional group part.

 

Cyclohexane

Cyclopentene

Methylcyclohexane

3-methylcyclohexene

 

Common Substituents for Hydrocarbons

  • In addition to the longest carbon chain, hydrocarbons can have ‘branches’ or formally – substituents. Substituents are denoted in the name as a prefix.

Substituent

Prefix

Example

Substituent

Prefix

Example

–CH3

Methyl-

2-Methylbutane

–Cl

Chloro-

chloroethane

–CH2CH3

Ethyl-

3-ethyl-2-methylhexane

–Br

Bromo-

bromoethane

–F

Fluoro-

Fluoroethane

–I

Iodo-

iodoethane

 IUPAC Rules for Naming

 

1.     Find the longest continuous carbon chain containing the principal functional group. This will help identify which carbons belong to a substituent group.

 

2-methylbutane

2.     Number the carbon chain such that the functional group receives the smallest number. After prioritising the functional group, the substituents should also receive the smallest number possible.

 

2-methyl-but-2-ene or 2-methyl-2-butene

3.     Name each substituent and indicate the position (separate by a ‘–‘)

 

4.     It two or more identical substituent groups are present, specify using the prefix:

 

di

Two identical groups

tri

Three identical groups

tetra

Four identical groups

 

2,3-dimethyl-2-butene

 

 

5.     If there are more than one substituent, arrange them in alphabetical order. If the sum of their positions remains the same, the first substituent (after rearrangement) should have the smaller number.

2-bromo-3-methyl-2-butene