Functional Groups

Functional groups

The way in which a compound will react is determined by a particular characteristic of a group of atoms and the way they are bonded (e.g. double C\(-\)C bond, C\(-\)OH group). This is called the functional group. This group is important in determining how a compound will react. The same functional group will undergo the same or similar chemical reaction(s) regardless of the size of the molecule it is a part of. Molecules can have more than one functional group.

In one group of organic compounds, called the hydrocarbons, the single, double and triple bonds between carbon atoms give rise to the alkanes, alkenes and alkynes, respectively. The double carbon-carbon bonds (in the alkenes) and triple carbon-carbon bonds (in the alkynes) are examples of functional groups.

In another group of organic compounds, called the alcohols, an oxygen and a hydrogen atom are bonded to each other to form the functional group (in other words an alcohol has an \(\text{OH}\) in it). All alcohols will contain an oxygen and a hydrogen atom bonded together in some part of the molecule.

The table below summarises some of the common functional groups. We will look at these in more detail later in this tutorial.

Name of group	Functional group	Example	Structural Formula
Alkane		Ethane
Alkene		Ethene
Alkyne		Ethyne
Haloalkane/alkyl halide		Chloromethane
Alcohol / alkanol		Methanol
Carboxylic acid		Methanoic acid

Table: Some functional groups of organic compounds.

There are some important points to note as we discuss functional groups:

• The beginning of a compound name (prefix) comes from the number of carbons in the longest chain:

  meth-	1 carbon atom
  eth-	2 carbon atoms
  prop-	3 carbon atoms
  but-	4 carbon atoms

• The end of a compound name (suffix) comes from the functional group, e.g. an alkane has the suffix -ane. Refer to the examples in the first table above.