Predicting E1, E2, Sn1, Sn2

tertiary halides

everything but Sn2

tertiary halide - strong base (-OH)

E2 only

tertiary halide - weak base/nu (H2O, R-OH)

Sn1/E1 mix

tertiary halide - weak base/strong nu (Br-)

Sn1 only

primary alkyl halides

Sn2 or E2

primary halide - strong nu (-OH, CH3O-)

Sn2 major

primary halide - strong bulky base, weak nu (t-butoxide)

E2 major

secondary halide

all mechanisms

secondary halide - strong base, strong nu (-OH)

Sn2/E2 mix

secondary halide - strong nu, weak base (Br-)

Sn2 only

secondary halide - strong bulky base, weak nu (t-butoxide)

E2 only

secondary halide - weak nu, weak base (H2O, R-OH)

Sn1/E1 mix

polar aprotic solvent

Sn2 and E2

polar protic solvent

Sn1 and E1

methyl halide substrate

Sn2 only

strong nu, weak base (I-, Br-, HS-, CN-)

Sn2 usu

bulky strong base, weak nu (t-butoxide, DBU, DBN)

E2 only