What is Organic Chemistry?

Organic chemistry is the branch of chemistry concerned with organic compounds. An organic compound contains one or more carbon-hydrogen (${\rm{C}{-}{H}}$) bonds. Because of the nature of a carbon atom and its ability to form four covalent bonds, there are a nearly infinite number of different compounds, in a huge variety of molecular configurations that include both long chains and ring structures. Organic compounds contribute to food, clothes, plastics, medicines, and soaps, as well as the molecules that build living organisms. These compounds are called organic compounds because living organisms are composed primarily of carbon-based compounds. In the early- to mid-nineteenth century, scientists thought that compounds derived from living, or organic, things were inherently different from those derived from nonliving, or inorganic, things. It is now known that the apparent differences between organic and inorganic compounds arise only from the arrangement of the atoms in the molecules, but the name remains.

While organic compounds also contain atoms such as oxygen, nitrogen, phosphorus, sulfur, and halogens, most organic compounds contain more carbon-hydrogen bonds than any other type of ${\rm{C}{-}{X}}$ bond. An organic compound that contains only carbon-carbon and carbon-hydrogen bonds is called a hydrocarbon. The four main classes of hydrocarbons are alkanes, alkenes, alkynes, and aromatics. An aliphatic compound is a hydrocarbon that contains only straight or branched carbon-carbon chains. Alkanes, alkenes, and alkynes are examples of aliphatic compounds. An aromatic compound is a planar hydrocarbon with C_nH_n stoichiometry that consists of alternating ${\rm{C}{-}{C}}$ and ${\rm{C}{=}{C}}$ bonds. Benzene (C₆H₆) is the smallest neutral carbon-only aromatic compound. An important facet of organic chemistry is the ability and tendency of carbon molecules to bond to atoms other than hydrogen. An atom or group of atoms (functional group) that replaces a ${\rm{C}{-}{H}}$ bond in an organic compound is called a substituent. Substituents can be several different kinds of atoms or groups of atoms, called functional groups. A functional group is a group of atoms with specific physical, chemical, and reactivity properties. When representing a functional group, an R is often used to indicate the remainder of the molecule that is not part of the functional group.

The skeletal structure of an organic compound is drawn using zigzag lines that represent carbon-carbon bonds. To save time, no ${\rm{C}{-}{C}}$ or ${\rm{C}{-}{H}}$ bonds are illustrated. In a skeletal structure, the carbon and hydrogen atoms are all implied, where each carbon atom has four bonds to it and a hydrogen atom is bonded to a single carbon center. There is an understanding that a carbon atom is located at every vertex of the zigzag, and every carbon atom is bound to four other atoms, so any bonds that are not drawn explicitly are assumed to be hydrogen atoms. Any atom or functional group that is not a carbon atom or a hydrogen atom has to be written.