A molecular species is covalently attached to elemental carbon by exposing the carbon to a reaction mixture containing a strong base and a compound of the formula or in which X denotes a covalently attached atom or group capable of forming an X− anion and each Z is a moiety comprising a plurality of atoms, but which does not have a hydrogen atom directly attached to the atom which itself is directly attached to the —CH2X or —CHX group. The carbon substrate may be graphite or carbon nanotubes.