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Ochem 2 > Chapter 16- Benzene and Derivatives > Flashcards

Chapter 16- Benzene and Derivatives Flashcards

1
Q

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

A

Substitution, electrophile

Called Electron Aromatic Substitution (EAS)

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2
Q

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

A

Electrophile

I’m these reactions Benzene is the nucleophile

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3
Q

Electrophiles are electron ________ or Lewis _______.

A

Acceptors, acids

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4
Q

Nitration….

A

E+ = NO2+

aryl H is replaced by… NO2

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5
Q

Sulfonation

A

E+ = SO3H+

aryl H is replaced by…. SO3H

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6
Q

Halogenation

A

E+ = X+

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

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7
Q

Friedel-Crafts Alkylation…

A

E+ = R+

aryl H is replaced by… an alkyl group -R

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8
Q

Friedel-Crafts Acylation

A

E+ = RCO+ (an acyl group)

aryl H is replaced by… RCO

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9
Q

What are three steps of reaction with Benzene?

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

*overall endergonic

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10
Q

Bromination

A

Br2 & FeBr3

Bromine attached to benzene and HBr

(Same three steps)

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11
Q

Chlorination

A

Cl2 & FeCl3

Cl attached to benzene ring & HCl

(Similar to bromination but slower)

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12
Q

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

A

H2O2, CuCl2

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13
Q

Iodination

A

I2 & CuCl2/H2O2

I attached to benzene ring & HI

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14
Q

Aromatic Nitration

A

HNO3 & H2SO4

NO2 attached to benzene and H2O

Three steps

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15
Q

Aromatic sulfonation

A

SO3/H2SO4

SO3H attached to benzene (benzenesulfonic acid)

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16
Q

Friedel-Crafts Alkylation

A

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

RCl/AlCl3

R group attached to benzene + HCl

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17
Q

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

A

FC Reactions

Pg. 240

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18
Q

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

A

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

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19
Q

What are some other problems with FC reactions?

A

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

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20
Q

No polysubstitution observed in…

A

FC- Acylation

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21
Q

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

A

Less, more

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22
Q

___ 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:

A

O-P

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23
Q

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

A

O-P directing groups and deactivators

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24
Q

O-P Directors and deactivators are all…..

A

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

25
Q

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.

A

Meta directors and deactivators

26
Q

All activating groups direct…

A

Ortho, para

27
Q

All halogen deactivating groups direct…

A

Ortho, para

28
Q

All non-halogen deactivators direct…

A

Meta

29
Q

The two factors that determine group orientation on the benzene ring

A
  • inductive effect

- Resonance effect

30
Q

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

A

Inductive

Alkyl groups inductively donate electrons, NO2 inductively withdraws electrons

31
Q

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

A

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

32
Q

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

A

Inductive electron withdrawing groups (EWG)

33
Q

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

A

Electron donating groups (EDG)

Halogens, -OH, NH2, -OR, -NR2

Pg. 254

34
Q 
EDG= \_\_\_\_\_\_ reactive 
EWG= \_\_\_\_\_\_ reactive
A

More, less

35
Q

Alkyl groups are…

A

Activators

36
Q

(-Z group) Z=O, N are….

A

Activators

37
Q

Halogens are…. 

A

Deactivators

38
Q

-Y=Zgroup (Z-=O,N) are…

A

Deactivators

39
Q

-NR3+ groups (R=Alkyl Group) are…

A

Deactivators

40
Q

CH3 is …..

A

An O-P directing group and activator

41
Q

-OH is ….

A

An O-P directing group and activator

42
Q

-Br is an ….

A

O-P directing group and deactivator

43
Q

-CHO is …

A

A meta directing group and deactivator

44
Q

-NH3+ is…

A

A meta-directing group and deactivator

45
Q

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

A

Mono-, ploy- (all ortho and para aryl Hs are replaced.

  • Assume the benzene is not overactive!
46
Q

Strong activating nitrogen containing groups _____ react. 

A

Do not.

 because these Lewis bases react with the catalyst AlCl3, A Lewis acid to give an intermediate deactivator

47
Q

No polysubstitution accounts with m…

A

FC acylation

48
Q

How do you avoid pollysubstitution?

A

Use an excess of benzene

49
Q

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

A

They reinforce each other and there is no conflict

50
Q

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

A

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

51
Q

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

A

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

52
Q

NAS process in two steps…

A
  • addition of Nu/elimination of the halogen

- it goes through a Meisenheimer complex (carbanion)

53
Q

How is NAS different from SN1 and SN2?

A

Instead of carbocation intermediate it’s Meisenhemier complex

54
Q

ESA:

A
  • Best for activating groups (EDG)
  • A carbocation intermediate is formed*
  • a H is replaced on benzene ring
  • a Two-step reaction: Addition/elimination
55
Q

NAS:

A

-Best with EWG in o-p

  • a Meisenheimer intermediate is involved
  • a halogen Is replaced on benzene ring
  • A two-step reaction: Addition/elimination
56
Q

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

A

Temperatures and high pressures

57
Q

Phenyl synthesis versus NAS

A

Phenol- elimination/Addition, benzene intermediate

NAS- Addition/Elimination, Meisenheimer intermediate

58
Q

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

A

Carboxylic acids

Ochem 2 (10 decks)

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