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Organic Chemistry > Aromatic Substitution Reaction > Flashcards

Aromatic Substitution Reaction Flashcards

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1
Q

Electrophilic aromatic substitution

A

Reaction in which one of the aromatic protons is replaced by an electrophile & the aromatic moiety is preserved

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2
Q

The presence of ________ in the reaction mixture enhances the electrophilicity of the bromine atom

A

Iron (Fe)

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3
Q

Iron reacts with bromine to make ______________ & is the catalyst in the reaction between benzene & bromine

A

Iron tribromide (FeBr3) (Lewis acid)

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4
Q

What is the mechanism for bromination of benzene?

A
  1. Formation of FeBr3
  2. Sigma complex (Arenium ion)
  3. Nucleophilic Attack
  4. Proton transfer
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5
Q

_____________ can also be used as a catalyst instead of FeBr3

A

Aluminum tribromide (AlBr3)

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6
Q

Substitution is an _____________ process (downhill in energy)

A

Exergonic

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7
Q

Addition is an ___________ process (uphill in energy)

A

Endergonic

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8
Q

_____________ of benzene can occur with Lewis acids such as AlBr3

A

Chlorination

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9
Q

What are the two general steps of benzene substitution reaction?

A
  1. The aromatic ring functions as a nucleophile & attacks ana electrophile to form a sigma complex
  2. Which is followed by deprotonation of the sigma complex to restore aromaticity
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10
Q

When benzene is treated with ____________ a sulfonation reaction occurs & benzene sulfuric acid is formed

A

Sulfuric Acid

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11
Q

The S=O bonds are seen as __________ bonds where sulfur has a partial positive charge & oxygen has a partial negative charge so sulfur is the electrophile that reacts with benzene

A

Single bonds

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12
Q

What is the mechanism of sulfonation of benzene?

A
  1. Nucleophilic attack
  2. Sigma complex
  3. Proton transfer
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13
Q

When benzene is treated with a mixture of nitric acid & sulfuric acid a _________ reaction occurs & nitrobenzene is formed

A

Nitration

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14
Q

A nitration reaction occurs via an electrophilic aromatic substitution in which a ___________ is the electrophile

A

Nitronium ion (NO2+)

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15
Q

What is the mechanism for nitration of benzene?

A
  1. Nucleophilic attack
  2. Sigma complex
  3. Proton transfer
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16
Q

The nitro in the nitrobenzene product can be reduced to give an __________

A

Amino group (NH2)

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17
Q

What are the two ways to install an amino group in a benzene ring?

A
  1. Nitration
  2. Followed by reduction of the nitro group
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18
Q

Friedel -crafts alkylation allows the installation of an __________ group on an aromatic ring

A

Alkyl group

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19
Q

A alkyl halide is treated with a lewis acid like aluminum trichloride to form a ___________ to react with benzene

A

Carbocation

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20
Q

What is the mechanism for Friedel-crafts alkylation?

A
  1. Formation of carbocation
  2. Nucleophilic attack
  3. Sigma complex
  4. Proton transfer
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21
Q

____ & ____ halides are readily converted into carbocation, but primary halides don’t form carbocations but can still react with benzene

A

20 & 30

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22
Q

What are the things to consider with a Friedel- craft alkylation?

A
  1. The carbon in the alkyl halide that is attached to the halogen must be Sp3
  2. Polyalkylation can occur but most of the time it’s under conditions that form monoalkylation
  3. Nitro groups can’t react in a Friedel-craft reaction
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23
Q

What type of substitutent group is this?

A

Acyl group

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24
Q

Acylation

A

Installs an acyl group (Friedel-crafts acylation) where the acyl group is treated with a Lewis acid to form an acylium ion

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25
Q

What is the mechanism for Friedel crafts acylation?

A
  1. Formation of the R-C+=O (Acylium ion)
  2. Nucleophilic attack
  3. Sigma complex
  4. Proton transfer
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26
Q

The product of a Friedel-craft acylation is an ___________ which can be reduced using a _________________

A

Aryl ketone, Clemmensen reduction

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27
Q

Nitration of toluene

A
  1. The methyl group in toluene in a nitration reaction is a ortho-para director
  2. For the regiochemistry ortho & para products dominate in this reaction
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28
Q

What does the methyl group in toluene do in a nitration reaction?

A

The methyl group on toluene activates the aromatic ring (which causes it to react faster than benzene) because the alkyl group is an electron donating via hyperconjugation & as a result the methyl group donate electron to the ring which stabilize the sigma complex & lower the activation energy

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29
Q

Ortho-para director

A

Means it causes the incoming nitro group into the ortho & para positions

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30
Q

Nitration of anisole

A

In the nitration of anisole, the para product is favored over the ortho product

31
Q

___________ is more activating than methyl group

A

Methoxy group (OCH3)

32
Q

In nitration of anisole there is competition between induction & resonance in anisole, whenever there’s competition between resonance & induction, _________ usually wins

A

Resonance

33
Q

____________suggest that methoxy group is electron withdrawing & __________ suggest that methoxy group is electron donating

A

Induction, Resonance

34
Q

All ____________ are ortho- para directors

A

Activators

35
Q

A _____ group deactivates the ring toward electrophilic aromatic substitution

A

Nitro

36
Q

The ______ group withdraws electrons because its resonance structures it has positive charges & by removing electron density form the ring it destabilizes the sigma complex & raises the energy of activation

A

Nitro

37
Q

________ groups in aromatic substitution makes a meta product dominate

A

Nitro

38
Q

A _______ group deactivates the ring & is a meta director

A

Nitro

39
Q

Most deactivators are _____ directors

A

Meta

40
Q

__________ are ortho-para directors & deactivates are meta director

A

Activators

41
Q

Many halogens such as Cl, Br, & I are __________ directors (They are electron withdrawing)

A

Ortho-Para

42
Q

When competition between resonance & induction occurs with halogen, ___________ wins because halogens withdraw electron density from the ring, thereby destabilizing the positively charge sigma complex & raising the energy of activation

A

Induction

43
Q

Both activators & deactivators can be classified as _________, _________, ________

A

Strong, moderate, weak

44
Q

Strong activators

A

Are characterized by the presence of a lone pair immediately adjacent to the aromatic ring

45
Q

Moderate activator

A

Exhibit a lone pair that is already delocalized outside the ring

46
Q

Alkoxy group are _________ activators

A

Moderate

47
Q

Alkyl groups are _______ activators because they donate electron density by the relatively weak effect of hyperconjugation

A

Weak

48
Q

Halogens are weak __________

A

Deactivators

49
Q

__________ deactivators are groups that exhibit a pie bond to an electronegative atom, where the pie bond is conjugated with the aromatic ring

A

Moderate

50
Q

How many strong activators are there?

A

3 (Look in notebook)

51
Q

In some cases the directing effects of all substituents _________ each other

A

Reinforce

52
Q

Sometimes substitutents can compete with each other where the more powerful (stronger) _________ group dominates

A

Activating

53
Q

For most monosubstituted aromatic rings the ____ product generally dominates over the ortho product as a result of steric effect

A

Para

54
Q

The regiochemistry outcome for 1,4-disubstituted aromatic rings is controlled by ________, where nitration is more likely to occur at a site that is less sterically hindered (ortho to a methyl group)

A

Steric effect

55
Q

For 1,3-disubstituted aromatic rings substituent will not occur at the position between ________ substituents because it’s the most sterically hindered position

A

Two

56
Q

A ________ group can be used to direct the bromination towards the ortho position

A

Blocking group (so blocking group is 1st installed at the para position)

57
Q

__________ is a common blocking group

A

Sulfonation (SO3H)

58
Q

The simplest kind of synthesis is the formation of ________________ benzene because you don’t need a directing affect just need to know what reagents to use for the desired product

A

Monosubstituted

59
Q

Nitration can’t be performed on a ring that contains an __________ group

A

Amino

60
Q

A friedel-crafts reaction (either alkylation or acylation) can’t be accomplished on rings that are either __________ or __________ deactivated. The ring must be either activated or weakly deactivated for a friedel-crafts reaction to occur

A

Moderately or strongly

61
Q

When dealing with polysusbtituted benzene ring its best to use ____________ approach

A

Retrosynthetic

62
Q

Electrophilic aromatic substitution

A

Reaction in which the aromatic ring attacks an electrophile

63
Q

Nucleophile aromatic substitution

A

A ring is attached by a nucleophile

64
Q

What are the criteria for a reaction to be a nucleophilic substitution reaction?

A
  1. The ring must contain a powerful electron withdrawing (usually a nitro group)
  2. The ring must contain a leaving group (usually a halide)
  3. The leaving group must be either ortho or para to the electron - withdrawing group. If the leaving group is meta to the nitro group then the reaction doesn’t happen
65
Q

For a nucleophilic substitution reaction to occur _________ must be met

A

All 3 criteria

66
Q

What is the mechanism for nucleophilic aromatic substitution (SNAr)

A
  1. Nucleophilic attack
  2. Meisenheimer complex
  3. Loss of Leaving group
67
Q

Elimination of H & Cl produces a very high energy intermediate called _________

A

Benzyne

68
Q

What is the mechanism for elimination - addition reaction?

A
  1. Proton transfer
  2. Loss of LG
  3. Nucleophilic attack
  4. Proton transfer
69
Q

What are the 3 different mechanism of an aromatic substitution reaction?

A
  1. Electrophilic aromatic substitution
  2. Nucleophilic aromatic substitution
  3. Elimination- Addition
70
Q

What are the few differences between all 3 mechanisms even though they are accomplish aromatic substitution?

A
  1. The intermediate
  2. Leaving group
  3. Substituent effect
71
Q

What is the difference between the intermediate in all 3 mechanism?

A

Electrophilic aromatic substitution occurs via a sigma complex, nucleophilic aromatic substitution occurs via Meisenheimer complex & elimination- addition occurs via benzyne intermediate

72
Q

What is the difference between the leaving group in all 3 mechanisms?

A

In an electrophilic aromatic substitution, the incoming substituent replaces a proton & the other two mechanism a negatively charge leaving group (Like halide ion) leaves

73
Q

What is the difference in substituent effect between all 3 mechanisms?

A

In electrophilic aromatic substitution, electron-withdrawing groups deactivate the ring toward attack, while in nucleophilic aromatic substitution an electron-withdrawing group is required for the reaction to occur

Organic Chemistry (47 decks)

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