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Hydrocarbon side groups

Side groups of only carbon and hydrogen in organic compounds have the same prefixes as the hydrocarbons, which you can find here. The suffix used is -yl.

If there are side groups on the longest chain of carbon atoms, these are numbered by the carbon they are attached to. The carbon number for this group of organic compounds is assigned so:

  • 1) You always count from one end of the longest carbon chain with the most important functional group
  • 2) If a double or triple bond is present, this should get the lowest number possible
  • 3) If only single bonds are present, the side groups should get the lowest number possible

If a side group can only be positioned in one place in the compound, the number can be omitted.

Check out the examples from the simulation in Figure 1 to see how the numbers are assigned:

There are 4 molecules. The first molecule is butane, C H 3, C H 2, C H 2, C H 3. Butane has an isomer called methyl propane, also known as isobutane. This molecule has the same number of carbon and hydrogen atoms but a different arrangement of them. The structure is similar to propane, C H 3, C H 2, C H 3, but one of the hydrogens bonded to the middle carbon is replaced with a methyl group, C H 3. The third molecule is hexane, C H 3, C H 2, C H 2, C H 2, C H 2, C H 3. Hexane has an isomer called 2,3-dimethyl butane. The structure is similar to butane, C H 3, C H 2, C H 2, C H 3, but two hydrogens, one bonded to the second carbon and one bonded to the third carbon, are replaced with methyl groups.

Figure 1. Examples of hydrocarbons with side groups.

Referred from:

Article
Nomenclature of simple hydrocarbons