What is the name for a five-carbon alkane?

A five-carbon alkane is properly named pentane. The nomenclature for alkanes follows a systematic naming convention established by IUPAC (International Union of Pure and Applied Chemistry). Alkanes are saturated hydrocarbons where each carbon atom is bonded to as many hydrogen atoms as possible, resulting in a formula of CnH2n+2.

In this case, the prefix "pent-" indicates the presence of five carbon atoms in the chain. Therefore, the molecular formula for pentane is C5H12, confirming that it is a saturated hydrocarbon with exactly five carbons. The suffix "-ane" is used for all alkanes, distinguishing them as saturated compounds.

Other relevant names in the question include hexane, which refers to a six-carbon alkane, octane, which is an eight-carbon alkane, and butane, which pertains to a four-carbon alkane. While these names denote other members of the alkane family, they do not apply to the five-carbon chain in this context. Thus, pentane is the correct identification for a five-carbon alkane.