Alkyl halides undergo nucleophilic substitution and elimination reactions. When the kinetics of the reaction are measured, if the rate of the reaction is found to be dependent upon the concentration of the nucleophile as well as the alkyl halide the reaction is second order. The substitution reaction is thus termed SN2, and the elimination reaction is termed E2. These reactions are bimolecular and take place in a single step. In the SN2 reaction, the nucleophile attacks the α-carbon from the backside and displaces the leaving group with an inversion of configuration occurring at the carbon. In the E2 elimination reaction, strong base removes an acidic hydrogen from the B-carbon and an alkene is formed as the leaving group is expelled from the α-carbon. This elimination follows Zaitsev’s rule whereby the more substituted alkene is generally formed. In E2 elimination, both the B-hydrogen and the leaving group must be oriented anti to each other. The same reaction conditions apply for both SN2 and E2, therefore these reactions often compete. Use of a strong, hindered base will tend to favor elimination, while use of a weak base/strong nucleophile will favor substitution. Draw curved arrows to show the movement of electrons in this step of the mechanism. Arrow-pushing Instructions