Alkyl group

An alkyl group is a monovalent group obtained formally by removing one hydrogen atom from an acyclic saturated hydrocarbon. The general composition is ${\mathrm{C}}_{\mathrm{n}}{\mathrm{H}}_{2n+1}$: examples include $\mathrm{C}{\mathrm{H}}_3-$ and $\mathrm{C}{\mathrm{H}}_3\mathrm{C}{\mathrm{H}}_2-$. The dash denotes an attachment chemical bond, rather than necessarily an unpaired electron.^[ref]

“Alkyl” specifies a structural fragment. The corresponding free radical, carbocation and carbanion have different electronic states and reactivities. Branched alkyl groups can also share an elemental formula while giving different connectivity and steric environments around the attachment site.