All organic compounds are made up of at least carbon and hydrogen. The most basic type of organic compound is one made up exclusively of sp3 carbons covalently bonded to other carbons and hydrogens through sigma bonds only. The generic name for this family of compounds is alkanes. Alkanes are part of a more general category of compounds known as hydrocarbons. Some hydrocarbons such as alkenes and alkynes contain sp2 or sp-hybridized carbon atoms.
Alkanes are of great importance to the different classification systems and the naming of organic compounds because they consist of a carbon chain that forms the main structural unit of all organic substances. When an alkane carbon chain is modified in any way, even by the mere introduction of an sp2 carbon or a heteroatom (atoms other than carbon and hydrogen), is said to be functionalized. In other words, a functional group has been introduced and a new class of organic substances has been created.
A functional group is a specific arrangement of certain atoms in an organic molecule that becomes the center of reactivity. That is, it is the portion of the structure that controls the reactivity of the entire molecule and much of its physical properties. An entire classificaton system of functional groups is based on atom hybridization. Some of these functional groups are presented on page 2. They are the most commonly studied in introductory organic chemistry courses.