= 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 $\mathrm{C_nH_{2n+1}}$: examples include $\mathrm{CH_3{-}}$ and $\mathrm{CH_3CH_2{-}}$. The dash denotes an attachment <chemical bond>, rather than necessarily an unpaired <electron>.<IUPAC Compendium of Chemical Terminology, fifth edition (Gold Book)>[Alkyl groups, entry A00228]{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.
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