Hydrocarbons are the simplest organic compounds . Containing only carbon and hydrogen, they can be straight-chain, branched chain, or cyclic molecules. Carbon tends to form four bonds in a tetrahedral geometry. Hydrocarbon derivatives are formed when there is a substitution of a functional group at one or more of these positions.

An almost unlimited number of carbon compounds can be formed by the addition of a functional group to a hydrocarbon.

Organic molecules containing a hydroxyl group are known as alcohols. Hydroxyl wiki.

Note that the carbonyl group is the functional group involved with several of the hydrocarbon derivatives shown above. Carbonyl wiki.

The carboxyl group is present in amino acids and carboxylic acids. Note that it is a hydroxyl group bonded to a carbonyl group. Carboxyl wiki.