Reactions

Question 1

a reaction that occurs at a sp^3 hybridized carbon can result in:

Answer 1

the substitution of one functional group by another

Question 2

nucleophilic substitution reaction

Answer 2

if the incoming functional group is a nucleophile that replaces the leaving group

Question 3

the nucleophile and leaving group can be:

Answer 3

charged (anionic) or neutral

Question 4

how are the two different mechanisms of nucleophilic substitution reactions different?

Answer 4

reaction kinetics

Question 5

Sn1

Answer 5

solvolysis reaction, rate=k[R-LG], independent of nucleophile concentration, first-order rate law, unimolecular rate-determining step

Question 6

rate of reaction for Sn1 depends on:

Answer 6

cation stability (activation energy), the rest is fast

Question 7

what are the trends for Sn1 reaction rates?

Answer 7

more stable cation = faster rate (can be altered by ARIO, R and I most important)

Question 8

optically pure halides can result in:

Answer 8

racemized products in Sn1 reaction (or any reaction where a carbocation intermediate is formed)

Question 9

how can carbocation intermediates be made more stable?

Answer 9

by rearrangement (ex. 1,2-hydride shift)

Question 10

Sn2

Answer 10

second order rate law, rate=k[CH3Br][OH-], bimolecular

Question 11

Sn2 rate of reaction depends on:

Answer 11

transition state (which cannot be isolated), generally only a single step

Question 12

what are the trends for Sn2 reaction rates?

Answer 12

reaction proceeds at a faster rate with a decrease in steric hinderance around the reactive carbon (leaving group)

Question 13

nucleophilic substitution that exhibit second-order kinetic behaviours are stereospecific and….

Answer 13

proceed with inversion of configuration

Question 14

primary alkyl halides react by:

Answer 14

Sn2 mechanism

Question 15

tertiary alkyl halides react by:

Answer 15

Sn1 mechanism

Question 16

Sn1 mechanism is favoured in the presence of:

Answer 16

a weak nucleophile

Question 17

Sn2 mechanism is favoured in the presence of:

Answer 17

a good nucleophile

Question 18

nucleophiles can be anions or neutral molecules, but they are all:

Answer 18

Lewis bases, or electron pair donors (must have a lone pair available) *basicity does not equate with nucleophilicity)

Question 19

For Sn1 reactions, the nucleophile is usually…

Answer 19

the solvent

Question 20

For Sn2 reactions, the nucleophile is usually:

Answer 20

anionic

Question 21

nucleophilicity

Answer 21

a measure of the reactivity of a nucleophile

Question 22

what kind of phenomena is nucleophilicity?

Answer 22

kinetic phenomena, rate of reaction depends on activation energy (whereas basicity is a thermodynamic phenomena)

Question 23

strength of nucleophile?

Answer 23

CARIO
Charge- anions better than neutral
Atom-larger atoms are better
Resonance-not involved in resonance=more available, better
Induction/Orbital- minor effect, lone pair should be as available as possible

Question 24

Sn1 reaction rates increase in:

Answer 24

polar solvents (helps stabilize formation of cation)

Question 25

Sn2 reaction rates increase in:

Answer 25

polar aprotic solvents (helps stabilize heterolytic bond breaking, less solvated so less intermolecular bonds to break, lower activation energy and stabilized transition state)

Question 26

aprotic solvents

Answer 26

do not have OH group

Question 27

how do increase rate of reaction of nucleophilic substitution by controlling leaving group

Answer 27

best leaving groups are WEAK BASE and POOR NUCLEOPHILE (so that reverse reaction is not favoured)

Question 28

OH- is a poor leaving group so....

Answer 28

rearrange to make a good leaving group (H2O-) and then make products (can be racemic)

Question 29

what are sulfonate esters good for?

Answer 29

act as good leaving groups in nucleophilic substitutions (helps to control against rearrangements)

Question 30

how to prepare sulfonate ester from alcohol

Answer 30

use sulfonate halide halide in the presence of a weak, non-nucleophilic organic base, to create sulfonate ester

Question 31

what are the most common sulfonate esters?

Answer 31

mesylate and tosylate (FAVOURS Sn2)