Sn2

Question 1

is Sn2 stereospecific?

Answer 1

yes

Question 2

how many steps are there?

Answer 2

1, concerted (same time)

Question 3

what is the rxn dependent on?

Answer 3

structure of substrate

strength of Nu

type of solvent

basicity of L.G.

Question 4

what does Sn2 stand for?

Answer 4

substitution, nucleophilic, bimolecular

Question 5

backside or frontside attack?

Answer 5

backside

Question 6

rate formula

Answer 6

rate = k[substrate][Nu] concentration based

transition state E determines rate

Question 7

inversion of configuration?

Answer 7

yes

Question 8

why not frontside?

Answer 8

too many e- repels

L.G. blocks from side (sterics)

Question 9

Nu EN trend

Answer 9

across row ——–> worse Nu, slower rxn

C > N > O > F

Question 10

Nu size trend

Answer 10

down group: better Nu, faster rxn

F < Cl < Br < I

this is opposite of the basicity trend

Question 11

solvent effects on size of Nu

Answer 11

if small Nu, polar solvent surrounds it and makes it unable to reach E+

Question 12

resonance effects on nucleophilicity

Answer 12

resonance makes e- less available to donate, therefore if there is resonance, worse Nu

Question 13

steric hinderance

Answer 13

1 problem in Sn2

Question 14

steric effects

Answer 14

Nu must be small enough to approach E+

bulky Nu are better bases, easily abstract unhindered H+

Question 15

what does a leaving group do

Answer 15

polarizes C-X bond, making an E+

leaves with pair of e-

Question 16

better L.Gs should…

Answer 16

be EN (to polarize bond)

be stable, less reactive conj bases (weak base)

Question 17

alkyl halide L.G. trend

Answer 17

tosylate > I > Br > Cl > F > CN

Question 18

bad L.G.s

Answer 18

OH- > H2N- > RO-

Question 19

effect of polarization

Answer 19

e- are squishy, stabilizes t.s.

Question 20

L.G. effect on t.s

Answer 20

better L.G. stabilizes t.s. by lowering Ea

Question 21

substrate most important factor

Answer 21

steric hinderance

CH3 > 1st > 2nd > 3rd (never happens)

Question 22

branching of beta carbon…

Answer 22

slows rxn, makes high t.s, increased Ea

Question 23

why do Sn2 need polar solvents?

Answer 23

to dissolve Nu-salt

Question 24

polar protic solvent

Answer 24

acidic H+

rate is lowered due to solvation

Question 25

polar aprotic solvent

Answer 25

doesn’t solvate Nu

rate faster, nucleophilicity better

may not fully dissolve Nu-salt