The overall result of an elimination reaction is the opposite of an addition reaction. In contrast, elimination reactions are often more closely related mechanistically to substitution reactions than to addition reactions. Elimination reactions are closely related mechanistically to substitution reactions, and are often in competition with them in the reaction mixture. The principal types of elimination reactions are α-elimination (1,1-elimination), in which the eliminated parts are geminal; α-elimination (1,2-elimination), in which they are vicinal; γ-elimination (1,3-elimination), in which a three membered-ring is formed; and an extrusion reaction, in which there is no overall change in the degree of unsaturation, nor is there the formation of a ring. In a general elimination reaction, usually two new molecules (often of unequal size) are formed from the original molecule. Furthermore, one of the resultant molecules usually has a greater degree of unsaturation than was present initially in the original molecule.