Organic compounds are organized into families. The members of the simplest hydrocarbon family are referred to as alkanes and have only singly bonded carbon (these can be represented as R–H where R represents a hydrocarbon group).
In other hydrocarbon families (alkenes and alkynes) at least one pair of carbons is joined by a multiple bond. This multiple bond is the reactive site in the molecule and is known as the functional group. The general formula of members of other families is shown below. These have functional groups containing atoms other than C and H.
Note that three of these families have the carbonyl group (C=O) as a common structural element.
In other hydrocarbon families (alkenes and alkynes) at least one pair of carbons is joined by a multiple bond. This multiple bond is the reactive site in the molecule and is known as the functional group.
Note that three of these families have the carbonyl group (C=O) as a common structural element.
| RH alkane | R–OH alcohol | .gif){kind=small} ketone |
| R2C=CR2 alkene | R–OR ether |  aldehyde |
| R2C≡CR2 alkyne R = H or hydrocarbon for alkenes, aldehydes, carboxylic acids. Otherwise R = hydrocarbon group. |  carboxylic acid |