alkyl group, in chemistry, group of carbon and hydrogen atoms derived from an alkane molecule by removing one hydrogen atom (see radical). The name of the alkyl group is derived from the name of its alkane by replacing the -ane suffix with -yl, e.g., methyl, CH₃, from methane, CH₄, and ethyl, C₂H₅, from ethane, C₂H₆. In some cases different alkyl groups can be formed from the same alkane by removing different hydrogen atoms; the alkyl groups are then distinguished by adding a prefix, e.g., 1-propyl or n-propyl, CH₂CH₂CH₃, and 2-propyl or isopropyl, CH(CH₃)₂, both formed from propane, CH₃CH₂CH₃. When a functional group is joined with an alkyl group, replacing the hydrogen that was removed, a compound is formed whose characteristics depend largely on the functional group.