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:

• Normal butyl or n-Butyl: CH₃–CH₂–CH₂–CH₂– (fully systematic name: butyl)
• Secondary butyl or sec-Butyl: CH₃–CH₂–CH(CH₃)– (fully systematic name: 1-methylpropyl)

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

• Isobutyl: (CH₃)₂CH–CH₂– (fully systematic name: 2-methylpropyl)
• Tertiary butyl, tert-Butyl or t-butyl: (CH₃)₃C– (fully systematic name: 1,1-dimethylethyl)