Functional groups give organic compounds their properties

A functional group is an atom or group of atoms that gives an organic compound its characteristic physical and chemical properties.

There are millions of known organic compounds, including both natural compounds produced by living organisms and synthetic ones created in labs. New organic compounds are constantly being synthesised in pharmaceutical and industrial settings, as well as in research universities.

Classes of organic compounds are based on functional groups

All organic compounds are classified into classes based on the specific functional groups present in their molecules. Compounds within the same class have similar chemical properties due to their common functional group(s).

Some key functional groups and their corresponding classes are summarised in the table below. The "R" groups represent any carbon-containing group and are used to write general formulas for classes of compounds. Carbon-containing groups with no additional functional groups are called alkyl groups.

Saturated vs. unsaturated hydrocarbons

Organic compounds can also be classified as saturated or unsaturated based on the types of carbon-carbon bonds present:

• In a saturated compound, all the carbon–carbon bonds are single. The simplest saturated hydrocarbon is methane (CH₄) - a member of the alkane family.
• In an unsaturated hydrocarbon, the main carbon chain must contain at least one carbon–carbon double or triple bond.
• Hydrocarbons with carbon–carbon double bonds are called alkenes. The simplest alkene is ethene (H₂C=CH₂).
• Hydrocarbons with carbon–carbon triple bonds are called alkynes. The simplest alkyne is ethyne (HC≡CH).

Alkanes, alkenes, and alkynes are all examples of aliphatic compounds. Aliphatic compounds are defined as lacking aromatic rings in their structures. In other words, their carbon frameworks are composed of linear chains, branched chains, or non-aromatic rings.