Cyclohexane
From Memory Alpha, the free Star Trek reference
Cyclohexane is a hydrocarbon comprised of six carbon atoms and twelve hydrogen atoms (C6H12).
Cyclohexane comprised one of the atmospheric layers of a Class 7 gas giant planet discovered by the Enterprise NX-01 in 2151. The cyclohexane layer was just above a layer of liquid phosphorus, which was unexpected. (ENT: "Broken Bow")
