Cyclononane is an alicyclic hydrocarbon consisting of a ring of nine carbon atoms. Its molecular formula is C<sub>9</sub>H<sub>18</sub>.
At 20 ðC, cyclononane, under the action of aluminum chloride, isomerizes to propylcyclohexane, and at 50 ðC to trimethylcyclohexanes.[6] On platinized carbon, cyclononane forms a mixture of indane and methylbenzene with other aromatic hydrocarbons.