Chapter 16- Benzene and Derivatives

Question 1

Benzene undergoes ___________ reactions in which an aryl H atom is replaced by an ___________.

Answer 1

Substitution, electrophile

Called Electron Aromatic Substitution (EAS)

Question 2

The reactivity of benzene stems from the 6 pi electrons that are sterically accessible, exposed and available to an incoming _________.

Answer 2

Electrophile

I’m these reactions Benzene is the nucleophile

Question 3

Electrophiles are electron ________ or Lewis _______.

Answer 3

Acceptors, acids

Question 4

Nitration….

Answer 4

E+ = NO2+

aryl H is replaced by… NO2

Question 5

Sulfonation

Answer 5

E+ = SO3H+

aryl H is replaced by…. SO3H

Question 6

Halogenation

Answer 6

E+ = X+

aryl H is replaced by… a halogen X (Cl,Br, I)

Question 7

Friedel-Crafts Alkylation…

Answer 7

E+ = R+

aryl H is replaced by… an alkyl group -R

Question 8

Friedel-Crafts Acylation

Answer 8

E+ = RCO+ (an acyl group)

aryl H is replaced by… RCO

Question 9

What are three steps of reaction with Benzene?

Answer 9

1. (Rate determining) make the E+ (endergonic)
2. Formation of a Carbocation (exergonic)
3. Reestablishment of the aromatic ring

*overall endergonic

Question 10

Bromination

Answer 10

Br2 & FeBr3

Bromine attached to benzene and HBr

(Same three steps)

Question 11

Chlorination

Answer 11

Cl2 & FeCl3

Cl attached to benzene ring & HCl

(Similar to bromination but slower)

Question 12

I2 alone is not reactive, it requires ___________ & ________.

Answer 12

H2O2, CuCl2

Question 13

Iodination

Answer 13

I2 & CuCl2/H2O2

I attached to benzene ring & HI

Question 14

Aromatic Nitration

Answer 14

HNO3 & H2SO4

NO2 attached to benzene and H2O

Three steps

Question 15

Aromatic sulfonation

Answer 15

SO3/H2SO4

SO3H attached to benzene (benzenesulfonic acid)

Question 16

Friedel-Crafts Alkylation

Answer 16

An aryl H is replaced with an alkyl(methyl, proyl etc.) group

RCl/AlCl3

R group attached to benzene + HCl

Question 17

Aryl halides are vinylic galaxies and do not undergo ____________ since the intermediate is highly unstable

Answer 17

FC Reactions

Pg. 240

Question 18

Benzene with ………. Cannot undergo FC rxn because these groups deactivate the benzene ring, making it less reactive.

Answer 18

Strongly electron withdrawing meta deactivators groups (-NO2, -CN, SO3H, etc.)
Same effect with meta -NH2 groups
Pg. 240

Question 19

What are some other problems with FC reactions?

Answer 19

Polyalkation, rearrangement due to a hydride or methyl shift that leads to a mixture of products. 

Question 20

No polysubstitution observed in…

Answer 20

FC- Acylation

Question 21

In substitution aromatic reactions, R effects the reaction by either making the ring _______ reactive (R=deactivator=EWG), or more _______ reactive (R= activator=EDG)

Answer 21

Less, more

Question 22

___ directors and activators have only single bonds and on neutral atoms of the Group that is directly attached to the ring, except phenyl.
In general, Thea groups are: -R(alkyl group) or -Z:

Answer 22

O-P

Question 23

They make the Monosubstituted ring less reactive than benzene. Overall they instruct the incoming group to go ortho and para

Answer 23

O-P directing groups and deactivators

Question 24

O-P Directors and deactivators are all…..

Answer 24

Halogens: -F, -Cl, -Br, -I

Question 25

Have a double bond, or triple bond, or a + or a delta+ on the atom of the group that is directly attached to the ring.

Answer 25

Meta directors and deactivators

Question 26

All activating groups direct…

Answer 26

Ortho, para

Question 27

All halogen deactivating groups direct…

Answer 27

Ortho, para

Question 28

All non-halogen deactivators direct…

Answer 28

Meta

Question 29

The two factors that determine group orientation on the benzene ring

Answer 29

- inductive effect | - Resonance effect

Question 30

___________ effect is the withdrawal or donation of electrons by a group through a sigma bond.

Answer 30

Inductive Alkyl groups inductively donate electrons, NO2 inductively withdraws electrons

Question 31

___________ effect is the withdrawal or donations of electrons by a group through a pi bond. 

Answer 31

Resonance It usually occurs with groups having lone pairs or pi bonds. For instance, -OH Has an electron donating resonance affect and -NO2 Has an electron withdrawal resonance effect

Question 32

When a group that contains an atom that is more electronegative than carbon: (nitrogen, oxygen, halogen)

Answer 32

Inductive electron withdrawing groups (EWG)

Question 33

These are groups that place a negative charge on the benzene ring through resonance

Answer 33

Electron donating groups (EDG) Halogens, -OH, NH2, -OR, -NR2 Pg. 254

Question 34

``` EDG= ______ reactive EWG= ______ reactive ```

Answer 34

More, less

Question 35

Alkyl groups are…

Answer 35

Activators

Question 36

(-Z group) Z=O, N are….

Answer 36

Activators

Question 37

Halogens are…. 

Answer 37

Deactivators

Question 38

-Y=Zgroup (Z-=O,N) are…

Answer 38

Deactivators

Question 39

-NR3+ groups (R=Alkyl Group) are…

Answer 39

Deactivators

Question 40

CH3 is …..

Answer 40

An O-P directing group and activator

Question 41

-OH is ….

Answer 41

An O-P directing group and activator

Question 42

-Br is an ….

Answer 42

O-P directing group and deactivator

Question 43

-CHO is …

Answer 43

A meta directing group and deactivator

Question 44

-NH3+ is…

Answer 44

A meta-directing group and deactivator

Question 45

With EAS reactions… with halogens, in absence of a catalyst it is _____halogenation In the presence of a Catalyst, it is _____halogenation.

Answer 45

Mono-, ploy- (all ortho and para aryl Hs are replaced. * Assume the benzene is not overactive!

Question 46

Strong activating nitrogen containing groups _____ react. 

Answer 46

Do not.  because these Lewis bases react with the catalyst AlCl3, A Lewis acid to give an intermediate deactivator

Question 47

No polysubstitution accounts with m…

Answer 47

FC acylation

Question 48

How do you avoid pollysubstitution?

Answer 48

Use an excess of benzene

Question 49

What happens when there are two groups with the same directing effects

Answer 49

They reinforce each other and there is no conflict

Question 50

What happens when there are two groups with opposing directing effects?

Answer 50

The more powerful activator takes over (major product) and you have a mixture of products 

Question 51

Disubstituted aryl halides can act as ________ and undergo _______ reactions.

Answer 51

Electrophiles, and nucleophilic reactions NAS Nucleophilic aromatic substitution reactions (Halogen is replaced by electron withdrawing group in ortho or para position) -only aryl halides with O-P EWG can react

Question 52

NAS process in two steps…

Answer 52

- addition of Nu/elimination of the halogen | - it goes through a Meisenheimer complex (carbanion)

Question 53

How is NAS different from SN1 and SN2?

Answer 53

Instead of carbocation intermediate it’s Meisenhemier complex

Question 54

ESA:

Answer 54

- Best for activating groups (EDG) - A carbocation intermediate is formed* - a H is replaced on benzene ring - a Two-step reaction: Addition/elimination

Question 55

NAS:

Answer 55

-Best with EWG in o-p - a Meisenheimer intermediate is involved - a halogen Is replaced on benzene ring - A two-step reaction: Addition/elimination

Question 56

Aryl halides with no o-p EWG  can be forced to react at high….

Answer 56

Temperatures and high pressures

Question 57

Phenyl synthesis versus NAS

Answer 57

Phenol- elimination/Addition, benzene intermediate NAS- Addition/Elimination, Meisenheimer intermediate

Question 58

Alkyl Side chains with a benzilic hydrogen react readily with oxidizing agents to give…

Answer 58

Carboxylic acids