When given an alkyl halide, depending on the reagent (strong nucleophile, weak nucleophile, strong base, or weak base), the reaction can undergo SN1, SN2, E1, or E2 mechanisms, right? I know SN1 and SN2 reactions require nucleophiles, while E1 and E2 reactions requires bases. My question: If given an alkyl halide and a reagent, how do you determine whether the reagent is a nucleophile or a base? This is confusing to me because the reagent can be both a nucleophile and a base at the same time. If a reagent has the properties of both a nucleophile and a base, how do you tell whether to use SN1, SN2, E1, or E2? The University of Colorado has a flow chart regarding this topic: http://walba.colorado.edu/substitution%20and%20elim'n%20'02.htm The University of Eastern Illinois also has one: http://www.ux1.eiu.edu/~cfthb/classes/2440/subst_elim.htm Still, I am stumped on how to differentiate between a nucleophile reagent or a basic reagent. Can you help me out here? If not, can you point me in the right direction? Thank you for your time.