Chapter 16- Benzene and Derivatives Flashcards
Benzene undergoes ___________ reactions in which an aryl H atom is replaced by an ___________.
Substitution, electrophile
Called Electron Aromatic Substitution (EAS)
The reactivity of benzene stems from the 6 pi electrons that are sterically accessible, exposed and available to an incoming _________.
Electrophile
I’m these reactions Benzene is the nucleophile
Electrophiles are electron ________ or Lewis _______.
Acceptors, acids
Nitration….
E+ = NO2+
aryl H is replaced by… NO2
Sulfonation
E+ = SO3H+
aryl H is replaced by…. SO3H
Halogenation
E+ = X+
aryl H is replaced by… a halogen X (Cl,Br, I)
Friedel-Crafts Alkylation…
E+ = R+
aryl H is replaced by… an alkyl group -R
Friedel-Crafts Acylation
E+ = RCO+ (an acyl group)
aryl H is replaced by… RCO
What are three steps of reaction with Benzene?
- (Rate determining) make the E+ (endergonic)
- Formation of a Carbocation (exergonic)
- Reestablishment of the aromatic ring
*overall endergonic
Bromination
Br2 & FeBr3
Bromine attached to benzene and HBr
(Same three steps)
Chlorination
Cl2 & FeCl3
Cl attached to benzene ring & HCl
(Similar to bromination but slower)
I2 alone is not reactive, it requires ___________ & ________.
H2O2, CuCl2
Iodination
I2 & CuCl2/H2O2
I attached to benzene ring & HI
Aromatic Nitration
HNO3 & H2SO4
NO2 attached to benzene and H2O
Three steps
Aromatic sulfonation
SO3/H2SO4
SO3H attached to benzene (benzenesulfonic acid)
Friedel-Crafts Alkylation
An aryl H is replaced with an alkyl(methyl, proyl etc.) group
RCl/AlCl3
R group attached to benzene + HCl
Aryl halides are vinylic galaxies and do not undergo ____________ since the intermediate is highly unstable
FC Reactions
Pg. 240
Benzene with ………. Cannot undergo FC rxn because these groups deactivate the benzene ring, making it less reactive.
Strongly electron withdrawing meta deactivators groups (-NO2, -CN, SO3H, etc.)
Same effect with meta -NH2 groups
Pg. 240
What are some other problems with FC reactions?
Polyalkation, rearrangement due to a hydride or methyl shift that leads to a mixture of products. 
No polysubstitution observed in…
FC- Acylation
In substitution aromatic reactions, R effects the reaction by either making the ring _______ reactive (R=deactivator=EWG), or more _______ reactive (R= activator=EDG)
Less, more
___ 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:
O-P
They make the Monosubstituted ring less reactive than benzene. Overall they instruct the incoming group to go ortho and para
O-P directing groups and deactivators
O-P Directors and deactivators are all…..
Halogens: -F, -Cl, -Br, -I
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.
Meta directors and deactivators
All activating groups direct…
Ortho, para
All halogen deactivating groups direct…
Ortho, para
All non-halogen deactivators direct…
Meta
The two factors that determine group orientation on the benzene ring
- inductive effect
- Resonance effect
___________ effect is the withdrawal or donation of electrons by a group through a sigma bond.
Inductive
Alkyl groups inductively donate electrons, NO2 inductively withdraws electrons
___________ effect is the withdrawal or donations of electrons by a group through a pi bond. 
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
When a group that contains an atom that is more electronegative than carbon: (nitrogen, oxygen, halogen)
Inductive electron withdrawing groups (EWG)
These are groups that place a negative charge on the benzene ring through resonance
Electron donating groups (EDG)
Halogens, -OH, NH2, -OR, -NR2
Pg. 254
EDG= \_\_\_\_\_\_ reactive EWG= \_\_\_\_\_\_ reactive
More, less
Alkyl groups are…
Activators
(-Z group) Z=O, N are….
Activators
Halogens are…. 
Deactivators
-Y=Zgroup (Z-=O,N) are…
Deactivators
-NR3+ groups (R=Alkyl Group) are…
Deactivators
CH3 is …..
An O-P directing group and activator
-OH is ….
An O-P directing group and activator
-Br is an ….
O-P directing group and deactivator
-CHO is …
A meta directing group and deactivator
-NH3+ is…
A meta-directing group and deactivator
With EAS reactions… with halogens, in absence of a catalyst it is _____halogenation
In the presence of a Catalyst, it is _____halogenation.
Mono-, ploy- (all ortho and para aryl Hs are replaced.
- Assume the benzene is not overactive!
Strong activating nitrogen containing groups _____ react. 
Do not.
 because these Lewis bases react with the catalyst AlCl3, A Lewis acid to give an intermediate deactivator
No polysubstitution accounts with m…
FC acylation
How do you avoid pollysubstitution?
Use an excess of benzene
What happens when there are two groups with the same directing effects
They reinforce each other and there is no conflict
What happens when there are two groups with opposing directing effects?
The more powerful activator takes over (major product) and you have a mixture of products 
Disubstituted aryl halides can act as ________ and undergo _______ reactions.
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
NAS process in two steps…
- addition of Nu/elimination of the halogen
- it goes through a Meisenheimer complex (carbanion)
How is NAS different from SN1 and SN2?
Instead of carbocation intermediate it’s Meisenhemier complex
ESA:
- Best for activating groups (EDG)
- A carbocation intermediate is formed*
- a H is replaced on benzene ring
- a Two-step reaction: Addition/elimination
NAS:
-Best with EWG in o-p
- a Meisenheimer intermediate is involved
- a halogen Is replaced on benzene ring
- A two-step reaction: Addition/elimination
Aryl halides with no o-p EWG  can be forced to react at high….
Temperatures and high pressures
Phenyl synthesis versus NAS
Phenol- elimination/Addition, benzene intermediate
NAS- Addition/Elimination, Meisenheimer intermediate
Alkyl Side chains with a benzilic hydrogen react readily with oxidizing agents to give…
Carboxylic acids
