lecture 5

Question 1

benzene + normal bromine

Answer 1

no reaction

Question 2

benzene and mcPBA

Answer 2

no reaction

Question 3

why can’t bromine and mCPBA react with benzene

Answer 3

bc benzene is aromatic, more stable
- cyclic
- conjugated
- flat
- huckels rule

Question 4

what happens to e- when they are conjugated

Answer 4

they are shared between the double bonds that are conjugated

they are shared between the system

this can be shown in resonance forms

Question 5

what must happen to bromine in order to react with benzene

Answer 5

it must be activated

Question 6

explain how bromine is activated

Answer 6

Br2 must react with a lewis acid

Question 7

what is a lewis acid

Answer 7

electron deficient
accepts e-

Question 8

what lewis acid is used to activate a bromine

Answer 8

AlCl3

aluminium tri chloride

Question 9

how is bromine activated using AlCl3

Answer 9

Bromine lone pair attacks the Al in AlCl3

Question 10

product of bromine activation with AlCl3 (lewis acid)

Answer 10

Br-Br- Al-Cl3
+ -

Question 11

how does AlCl3 activate bromine

Answer 11

the lewis acid weakens the Br-Br bond by removing some e- density

allowing it to react with aromatics

Question 12

draw the reaction between aromatics and an activated bromine

Answer 12

• aromatic arrow to bromine
• bromine arrow to the + Bromine
• the 2 products are a CC+ cyclohexene with a bromine attached and a Br-Al-Cl3 molecule

Question 13

what can occur in the product when aromatics react with an activated bromine

Answer 13

the CC+ cyclohexene bromine can have resonance forms in the molecule. (it is no longer aromatic)
the Br-AlCl3 has a - charge on the Al

Question 14

what is needed in order for the cc+ cyclohexene with bromine attached to regain its aromaticity

Answer 14

it needs to have a proton removed

Question 15

how does cc+ cyclohexene with bromine regain its aromaticity

Answer 15

it loses a Hydrogen

the e- in the Br-Al bond in Br-Al-Cl3 attack the H which gives its electrons to the ring, regaining its aromaticity

Question 16

okay so steps of the reaction of bromine with an aromatic

Answer 16

• bromine + Al-Cl3 gives Br-Br(+)-Al(-) -Cl3
• the double bond then attacks one br giving Br-Al(-)-Cl3
• the Br-Al then attacks the H giving HBr, AlCl3 (-) and an aromatic

Question 17

what is needed for a normal nitration reaction

Answer 17

HNO3 (nitric acid)

Question 18

can nitric acid HNO3 react with an aromatic

Answer 18

nope!!
it must first be activated

Question 19

how is nitric acid, HNO3 activated

Answer 19

it uses H2SO4 to protonate itself
lone pair on one O attacks the H of H2SO4
H e- are moved onto the O
- protonated HNO3 now has a H2O group (good LG)
- O- electrons kick off the H2O

Question 20

draw a nitric acid molecule

Answer 20

HNO3
+
-:O: - N = O
|
:O:H
(this one attacks the H in H2SO4)
and is later forced to leave

Question 21

when HNO3 reacts with H2SO4 it is activated,, what does this give

Answer 21

a very reactive electrophile
nitronium ion
+
O=N=O

Question 22

what is used to nitrate aromatics

Answer 22

activated HNO3 (nitric acid)
aka a nitronium ion ( O=+N=O)

Question 23

reaction between an aromatic and a nitronium ion step 1

Answer 23

double bond attacks the + charged N
e- are taken to the double bonded O

Question 24

reaction between an aromatic and a nitronium ion product of step 1

Answer 24

aromatic is bonded to the NO2
the N is +
the O is -

Question 25

step 3 of the reaction between an aromatic and a nitronium ion

Answer 25

the aromatic wants to regain the aromaticity lost when bonded to the NO2 so it loses a H and it’s e- are donated to the ring system, regenerating it’s aromaticity

Question 26

what is used to remove the H in the reaction of an aromatic and a nitronium ion in order for it to regain its aromaticity

Answer 26

a HSO4 (-) charged

Question 27

what is the final product of nitric acid // nitronium and a benzene aromatic

Answer 27

a nitrobenzene product benzene with NO2 bound to it

Question 28

benzene and nitric acid is called aaaaa

Answer 28

nitration reaction

Question 29

what is needed in a sulfonation reaction

Answer 29

2 H2SO4 in order to activate themselves

Question 30

how is H2SO4 activated in a sulfonation reaction

Answer 30

it uses another H2SO4 in order for one of the single bonded Os to gain a H by attacking it, this will give a H2O which can then be lost as a good LG (one step of attacking the H and the H2O leaving) the lone pairs on the other single O donate : to form a double bond with the S and neutralise it as it was +

Question 31

what is the final product when H2SO4 is activated

Answer 31

a protonated SO3 // HSO3 O(+) charged, S is neutral, other Os are neutral a strong electrophile which can react with aromatic

Question 32

how to remember the products

Answer 32

remember they have to be electrophiles so will probably have a + charge

Question 33

what does the aromatic attack in a sulfonation

Answer 33

it attacks the S in the middle the double bond e- then go to the newly made O(+) this O will have a + charge

Question 34

what is used to remove a H from the sulfonation product

Answer 34

the HSO4 (-) this helps it regain its aromaticity

Question 35

what is the product of the sulfonation of benzene

Answer 35

benzene sulfonic acid

Question 36

what is the RDS when the aromatic and the electrophile react

Answer 36

the rds is the breaking of aromaticity when the aromatic attacks the activated electrophile (SO3, NO2, Br-AlCl3)

Question 37

what is the fast step when an aromatic attacks an activated electrophile

Answer 37

the fast step is the regeneration of an aromatic when the H is removed rearomatisation

Question 38

electrophilic aromatic substitution reactions

Answer 38

bromination nitration sulfonation

Question 39

what is needed in a bromination reaction with an aromatic

Answer 39

Br2 AlCl3 combine

Question 40

what is needed in a nitration reaction with an aromatic

Answer 40

HNO3 H2SO4 nitronium ion

Question 41

what is needed in a sulfonation reaction

Answer 41

H2SO4 H2SO4

Question 42

when an aromatic attacks an electrophile,, what is made

Answer 42

a cyclohexene attached to the electrophile it has resonance forms as it is a CC+ intermediate

Question 43

what then occurs to the benzene x electrophile x CC+ intermediate

Answer 43

a hydrogen is removed in order to regain its aromaticity

Question 44

steps in electrophilic aromatic substitution

Answer 44

- activation of electrophile - attack of electrophile + CC+ intermediate formation - removal of H to regain aromaticity