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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.

Definition: Functional group

In organic chemistry a functional group is a specific group of atoms (and the bonds between them) that are responsible for the characteristic chemical reactions of those molecules.

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

8c90007079f6ebf5650d3d202d27a1e7.png

Ethane

ebd510dc2d6461b63cfc7f64d82da88e.png

Alkene

9549e726cee31ad4d610e8712e4ecd50.png

Ethene

28bebaf98de89c89a8068c4b6780f7f6.png

Alkyne

36b2fdd0222e7e246d44a4da8c27f060.png

Ethyne

724a200ee88b516e20369f0d891b96c7.png

Haloalkane/alkyl halide

71b20eb3fa6d64cbcb10bae1af25c6f3.png

Chloromethane

4c97ec6c2c4a42a46abc0aefc9c795bb.png

Alcohol / alkanol

581d1f3fa0c15f4502558e428de4bff4.png

Methanol

b1529fdb6697071c0712c3c5acd8ee1b.png

Carboxylic acid

9d8f492dfa1ca12fede2806c72452cee.png

Methanoic acid

4c911f1e01c01a8a1d2d5707e701cb61.png

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.

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