Definition of insertion

1. A chemical reaction or transformation of the general type

   X-Z + Y X-Y-Z

   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

   R3C-H + H2C: R3C-CH3

   The reverse of an insertion is called an extrusion. See also -addition.