The 5-carbon aliphatic group C5H11, also known as pentyl. Eight isomeric arrangements (exclusive of optical isomers) are possible. The amyl compounds occur (as in fusel oil) or are formed (as from the petroleum pentanes) as mixtures of several isomers, and, since their boiling points are close and their other properties similar, it is neither easy nor usually necessary to purify them.See Amyl Alcohol.