The reverse of an addition reaction or transformation. In an elimination two groups (called eliminands) are lost most often from two different centres (1/2/elimination or 1/3/elimination, etc.) with concomitant formation of an unsaturation in the molecule (double bond, triple bond) or formation of a new ring. If the groups are lost from a single centre (α-elimination, 1/1/elimination) the resulting product is a carbene or a 'carbene analogue'.