Butyl

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 of butane.

The isomer n-butane can connect either at one of the two terminal carbon atoms or at one of the two internal carbon atoms, giving rise to two "-butyl" groups:

The second, branched isomer of butane, isobutane, can connect either at one of the three terminal carbons or at the central carbon, giving rise to another two groups:

Nomenclature

According to IUPAC nomenclature, "isobutyl", "sec-butyl", and "tert-butyl" are all retained names.

Butyl is the largest substituent for which trivial names are commonly used for all isomers.