Substitution and Elimination Mechanisms Flashcards
Substitution or elimination?
Good nucleophiles, weak bases tend to favor substitution (X-,HS-,CN-,CH3COO)
Stereochemistry of SN2
Inversion around stereocenter due to backside attack of nucleophile
Reaction mechanism for
2° halide + strong base and nucleophile
SN2 and E2
Solvent for E2
Polar aprotic solvents
How to tell if E1 or E2?
For E2, both H and LG must be axial
Stronger bases favor which elimination?
E2
Reaction mechanism for
2° halide + strong, bulky base
E2
As # of R groups increase, rate of SN1…
Increases, 1° doesn’t occur
Solvent for E1
Polar protic solvents, have OH, NH, or a charge
Reaction mechanism for
2° halide + weak base and nucleophile
SN1 and E1
Reaction mechanism for
3° halide + strong base and nucleophile
E2
Reaction mechanism for
3° halide + weak base and nucleophile
Sn1 and E1
As # of R groups increase, rate of SN2…
Decreases, 3° doesn’t occur
Weaker bases favor which elimination?
E1
As # of R groups increases, the rate of E2…
Increases, all occur
Reaction mechanism for
1° halide + strong, bulky base
E2
As # of R groups increases, the rate of E1…
Increases, 1° doesn’t occur
Solvent for SN2
Polar aprotic solvents
Solvent for SN1
polar protic solvents
Stereochemistry of SN1
Racemic mixture, as Nu can approach from top or bottom
Zaitsev Rule
More substituted alkene is usually favored, but steric hindrance can lead to another major product
Reaction mechanism for
1° halide + strong nucleophile
SN2
