1. A chemical reaction or transformation of the general type:
    in which the connecting atom or group Y replaces the bond joining the parts X and Z of the reactant XZ. An example is the carbene insertion reaction:
    The reverse of an insertion is called an extrusion.
    See also: α-addition
    PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1125 (
  2. A general term given to a reaction involving the transfer of a guest atom, ion or molecule into a host crystal lattice.
    See: topochemical reaction, topotactic reaction, intercalation reaction
    PAC, 1994, 66, 577. 'Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)' on page 583 (