Substitution and Elimination Mechanisms

Question 1

Substitution or elimination?

Answer 1

Good nucleophiles, weak bases tend to favor substitution (X-,HS-,CN-,CH3COO)

Question 2

Stereochemistry of SN2

Answer 2

Inversion around stereocenter due to backside attack of nucleophile

Question 3

Reaction mechanism for
2° halide + strong base and nucleophile

Answer 3

SN2 and E2

Question 4

Solvent for E2

Answer 4

Polar aprotic solvents

Question 5

How to tell if E1 or E2?

Answer 5

For E2, both H and LG must be axial

Question 6

Stronger bases favor which elimination?

Answer 6

E2

Question 7

Reaction mechanism for
2° halide + strong, bulky base

Answer 7

E2

Question 8

As # of R groups increase, rate of SN1…

Answer 8

Increases, 1° doesn’t occur

Question 9

Solvent for E1

Answer 9

Polar protic solvents, have OH, NH, or a charge

Question 10

Reaction mechanism for
2° halide + weak base and nucleophile

Answer 10

SN1 and E1

Question 11

Reaction mechanism for
3° halide + strong base and nucleophile

Answer 11

E2

Question 12

Reaction mechanism for
3° halide + weak base and nucleophile

Answer 12

Sn1 and E1

Question 13

As # of R groups increase, rate of SN2…

Answer 13

Decreases, 3° doesn’t occur

Question 14

Weaker bases favor which elimination?

Answer 14

E1

Question 15

As # of R groups increases, the rate of E2…

Answer 15

Increases, all occur

Question 16

Reaction mechanism for
1° halide + strong, bulky base

Answer 16

E2

Question 17

As # of R groups increases, the rate of E1…

Answer 17

Increases, 1° doesn’t occur

Question 18

Solvent for SN2

Answer 18

Polar aprotic solvents

Question 19

Solvent for SN1

Answer 19

polar protic solvents

Question 20

Stereochemistry of SN1

Answer 20

Racemic mixture, as Nu can approach from top or bottom

Question 21

Zaitsev Rule

Answer 21

More substituted alkene is usually favored, but steric hindrance can lead to another major product

Question 22

Reaction mechanism for
1° halide + strong nucleophile

Answer 22

SN2