Hydrocarbons, in organic chemistry, are organic compounds consisting entirely of the elements carbon and hydrogen. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called "hydrocarbyls". Aromatic hydrocarbons (arenes), alkanes, alkenes, cycloalkanes, and alkyne-based compounds are different types of hydrocarbons.
The majority of hydrocarbons found naturally occur in crude oil, where decomposed organic matter provides an abundance of both carbon and hydrogen atoms, which can form seemingly endless chains of different hydrocarbons.
Isomerism, or isomers, is a phenomenon whereby 2 compounds share the same chemical formula while behaving differently with differing sets of physical and chemical properties. A German chemist, Johannes Wislicneus, suggested in 1873 that this is possible because of differences in the molecular structure or arrangement of atoms between the bonds. When the difference is due to molecular structure, this is called structural isomerism. When the difference is because of the arrangement of the atoms between the bonds, it is called stereoisomerism.