Endo-exo isomerism is a special type of isomerism found in organic compound

Organic compound

An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...

s with a substituent

Substituent

In organic chemistry and biochemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon...

 on a bridged ring system. The prefix endo is reserved for the isomer with the substituent located closest, or "syn," to the longest bridge. The prefix exo is reserved for the isomer with the substituent located farthest, or "anti," to the longest bridge. Here "longest" and "shortest" refer to the number of atoms that comprise the bridge. This type of molecular geometry

Molecular geometry

Molecular geometry or molecular structure is the three-dimensional arrangement of the atoms that constitute a molecule. It determines several properties of a substance including its reactivity, polarity, phase of matter, color, magnetism, and biological activity.- Molecular geometry determination...

 is found in norbornane

Norbornane

Norbornane is an organic compound and a saturated hydrocarbon with chemical formula C7H12. It is a crystalline compound with melting point 88 °C. The carbon skeleton is a cyclohexane ring bridged by a methylene group in the 1,4- position, and is a bridged bicyclic compound...

 systems such as dicyclopentadiene

Dicyclopentadiene

Dicyclopentadiene, abbreviated DCPD, is a chemical compound with formula C10H12. At room temperature, it is a white crystalline solid with a camphor-like odor. Its energy density is 10,975 Wh/l....

.

The terms endo and exo are used in a similar sense in discussions of the stereoselectivity in Diels-Alder reactions.