Pentane is an organic compound with the formula C₅H₁₂—that is, an alkane with five carbon atoms. The term may refer to any of three structural isomers, or to a mixture of them: in the IUPAC nomenclature, however, pentane means exclusively the n-pentane isomer; the other two are called isopentane and neopentane. Cyclopentane is not an isomer of pentane because it has only 10 hydrogen atoms where pentane has 12.