Sn2

Question 1

What is the one step substitution reaction called?

Answer 1

Sn2

Substitution, nucleophilic, 2nd rate

Question 2

How many steps in sn2?

Answer 2

One step

substitution, nucleophilic, 2nd rate

Question 3

What does 2nd rate reaction mean?

Answer 3

Both reagents are involved in the rate determining step

Question 4

Where does the nucleophile attack from in sn2?

Answer 4

180 degrees, from behind

Question 5

What substitution reaction mechanism attacks from behind? 180 degrees

Answer 5

sn2

Question 6

what undergoes sn2 reactions?

Answer 6

primary and secondary, aren’t sterically hindered

tertiary, aromatic and double bond to halogen (vinylic halide) don’t do sn2

Question 7

What doesn’t undergo sn2?

Answer 7

Tertiary
aromatic
double bond to halogen (vinylic halide)
all too sterically hindered

Question 8

Why do tertiary, aromatic and vinylic halides not undergo sn2 reactions?

Answer 8

They’re too sterically hindered

Question 9

For a reaction to proceed is gibbs free energy of products above or below zero?

Answer 9

below, releases energy

Question 10

What is transition state?

Answer 10

the combination of reagents, exists at energy maxima and extremely unstable

Question 11

Where is the transition state on an energy diagram?

Answer 11

at energy maxima

Question 12

what is transition state represented by?

Answer 12

double dagger (two plusses on-top of each other (‡ ))

Question 13

What is the rate of reaction determined by?

Answer 13

The activation energy

Question 14

What is the activation energy?

sn2

Answer 14

Energy required for a reaction to happen,

energy difference between starting and transition state

Question 15

How can you control rate of reaction?

Answer 15

Changing activation energy by:
Changing energy level of reactant
Changing energy level of transition state ( ‡ )

Question 16

What are solvent effects for sn2 reaction?

Answer 16

Adding polar solvent slows reaction.
Since sn2 involves anionic nucleophiles the polar solvent can stabilise these, lowering the starting materials energy, but not the transition state so more energy is needed to reach the transition state

Question 17

What does adding a polar solvent do to a sn2 reaction?

Answer 17

Slows it down since the polar solvent stabilises anionic nucleophiles lowering starting material energy, so more energy is needed to move it to transition state

Question 18

What are the steric effects of sn2 reactions?

Answer 18

The larger the substituents the slower the reaction.
Since transition state has ‘5 bonds’ its very sterically hindered, the more hindered it is the higher in energy it becomes, so more energy is needed to reach it.

Question 19

For an sn2 reaction what is faster a carbon with lots of substituents or a small one?

Answer 19

A small one is faster, since the transition state will be less sterically hindered, so lower in energy

Question 20

What materials does sn2 not happen with?

Answer 20

Tertiary carbons
Vinylic halides (double bond with halogen to one of the c’s)
Aromatic compounds
ALL TOO STERICALLY HINDERED cant approach from the back

Question 21

Order of reaction speed for sn2 steric effects

Fastest to slowest

Answer 21

Methyl> Primary> secondary

tertiary doesn’t happen too sterically hindered

Question 22

sn2 doesn’t occur on…

Answer 22

SP2 carbons

Question 23

What angle does nucleophile attack from in sn2?

Answer 23

180 degrees

Question 24

What are the electronic effects of sn2 reactions?

Answer 24

Stabilising transition state lowers it in energy, making it easier to reach. Conjugated systems can do this.