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:

• If it connects at one of the two terminal carbon atoms, it is normal butyl or n-butyl: −CH₂−CH₂−CH₂−CH₃ (preferred IUPAC name: butyl)
• If it connects at one of the non-terminal (internal) carbon atoms, it is secondary butyl or sec-butyl: −CH(CH₃)−CH₂−CH₃ (preferred IUPAC name: butan-2-yl)

The second isomer of butane, isobutane, can also connect in two ways, giving rise to two additional groups:

• If it connects at one of the three terminal carbons, it is isobutyl: −CH₂−CH(CH₃)₂ (preferred IUPAC name: 2-methylpropyl)
• If it connects at the central carbon, it is tertiary butyl, tert-butyl or t-butyl: −C(CH₃)₃ (preferred IUPAC name: tert-butyl)