Butyl group

In organic chemistry, butyl is a four-carbon alkyl radical or substituent group with general chemical formula −C4H9, derived from either of the two isomers (n-butane and isobutane) of butane.

The isomer n-butane can connect in two ways, giving rise to two "-butyl" groups: The second isomer of butane, isobutane, can also connect in two ways, giving rise to two additional groups: According to IUPAC nomenclature, "isobutyl", "sec-butyl", and "tert-butyl" used to be allowed retained names.

The names of enantiomers are: Therefore, for butyl acetate, the total number of isomers is five, if stereoisomers are included.

Alkyl radicals are often considered as a series, a progression sequenced by the number of carbon atoms involved.

In that progression, Butyl (containing 4 carbon atoms) is the fourth, and the last with preferred IUPAC name derived from its history.