Pyridine derivatives with one or more keto groups on the ring.

Butanes are flammable, colorless gases with a mild petroleum-like odor, consisting of either one of two isomeric forms of butane (n-butane or isobutane), used primarily as fuel, in the production of a wide range of chemicals, and as a refrigerant.

Changing an open-chain hydrocarbon to a closed ring. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)

Unsaturated hydrocarbons of the type Cn-H2n, indicated by the suffix -ene. (Grant & Hackh's Chemical Dictionary, 5th ed, p408)