An alkane graph is a tree in which vertices correspond to atoms and edges to carbon-carbon or hydrogen-carbon bonds in a chemical alkane. In chemistry, an alkane is an acyclic saturated hydrocarbon, meaning a molecule consisting of hydrogen and carbon atoms arranged in a tree structure in which all carbon-carbon bonds are single.
A linear alkane graph (sometimes called an n-alkane graph) is a straight-chain alkane graph. The first few are the methane graph (5-star graph), ethane graph, propane graph, butane graph, pentane graph, hexane graph, heptane graph, octane graph, nonane graph, and decane graph. Such graphs as also called caterpillar trees (Boesch et al. 1974; Merrifield and Simmons 1989, pp. 161-162), although a competing more general definition of caterpillar graph is also commonly used.
Linear alkane graphs are series-reduced trees.
Starting with butane, nonlinear isomers also exist. In particular, isobutane consists of a central carbon atom surrounded by three carbon atoms.