i.e., pure carbonium ion mechanism. Interpretation is provided by the relative strengths of the interaction between cation and halogen on the one hand and between anion and H o n the other. If the two interactions are comparable in strength, the E2 mechanism is found to operate; if interaction between cation and halogen is the stronger, the El mechanism is observed. Stereoselectivity decreases with rise in temperature.Polymerization of lactams by Brernsted acids (protic acids, ammonium salts, HzO) and by Lewis acids[1,2J can be