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Year 2 Chemistry OCR A level > AC3: Aromatics > Flashcards

AC3: Aromatics Flashcards

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1
Q

What are the 3 pieces of evidence that the structure of benzene is different to the Kekule model

A
  • Doesn’t undergo typical addition reactions of alkenes / doesn’t decolourise bromine
  • All the carbon to carbon bonds are the same length
  • Hydrogenation of benzene is less exothermic than expected by comparing it to alkenes
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2
Q

In benzene, how many sigma bonds does each carbon form

A

3 sigma bonds

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3
Q

In benzene, how many electrons does each carbon have in each orbital and what is the orbital

A

1 electron in the p orbital

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4
Q

In benzene, what is the system called when the orbital overlap

A

delocalised pi- electron system

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5
Q

Why does benzene have low reactivity

A

Delocalisation spreads out the pi-electrons more than they would be in a localised pi-bond, hence electron density is lower in aromatic compounds- so less attractive to electrophiles

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6
Q

Why are the bond lengths the same size in benzene

A

The pi-electrons are distributed evenly around the ring, hence all of the carbon-carbon bond lengths are the same

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7
Q

Why is the hydrogenation of benzene less exothermic than expected

A

Delocalisation lowers the energy of the pi-electrons (they are in a more stable state than electrons in a localised pi-bond). This means that reactions that break up the delocalised pi-electron system are less favourable than might have been expected.

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8
Q

What is an electrophile

A

An electron pair acceptor

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9
Q

Are aromatic or alkenes are more reactive

A

Alkenes since theur pi-electrons are localised so they have a higher electron density

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10
Q

Do aromatics tend to react by addition or substitution

A

Substitution since the delocalised pi-system is still present in the product

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11
Q

What are the conditions needed to nitrate the benzene ring

A
  • concentrated nitric acid
  • concentrated sulfuric acid
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12
Q

What is the name of the mechanism to nitrate the benzene ring

A

Electrophilic substitution

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13
Q

What are the 3 steps of the mechanism to nitrate the benzene ring

A
  • Formation of the electrophile
  • Reaction with the electrophile
  • Regeneration of the catalyst
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14
Q

When nitrating the benzene ring, what is the catalyst

A

The sulfuric acid

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15
Q

What type of reaction occurs between an aromatic compound and a halogen

A

Substitution

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16
Q

For a halogen to react with an aromatic compound, what is needed

A

A halogen carrier (catalyst)

17
Q

What are the 2 main halogen carriers

A

AlCl3 and FeCl3 , the Cl can be Br etc

18
Q

What are the 3 steps in the mechanism for halogenating an aromatic compound

A
  • The halogen carrier reacts with the halogen to produce an electrophile
  • Attack on the aromatic ring by the electrophile
  • The halogen carrier is regenerated by the releases H+
19
Q

What is the name of the mechanism between an aromatic compound and a halogen

A

Electrophilic substitution

20
Q

How is an alkyl group attached to the benzene ring / what type of reaction

A

By electrophilic substitution

21
Q

To attach an alkyl group to the benzene ring, what type of catalyst is needed

A

Halogen carrier

22
Q

What are the 3 steps in the mechanism when attaching an alkyl group to the benzene ring

A
  • Halogen carrier generates an electrophile
  • Electrophile attaches aromatic ring
  • Catalyst is regenerated
23
Q

Why is added an alkyl group to an aromatic compound important in organic synthesis

A

Because they form carbon to carbon bonds, allowing for the framework of organic molecules to extend

24
Q

When you add an acyl chloride to an aromatic compound, what is the product

A

Aromatic ketone

25
Q

When adding an acyl chloride to an aromatic compound, what type of catalyst is needed

A

Halogen carrier

26
Q

What are the 3 steps in the mechanism when adding an acyl chloride to an aromatic compound

A
  • Halogen carrier forms an electrophile
  • The electrophile attacks the aromatic ring
  • The catalyst is regenerated
27
Q

If a benzene is substituted into a molecule, what is the name of the prefix of the molecule

A

Phenyl

28
Q

What is any compound that contains a benzene ring classified as

A

Aromatic

29
Q

What is any compound that does not contain a benzene ring classified as

A

Aliphatic

30
Q

What is any aliphatic compound that contains a ring (non-aromatic) classified as

A

Alicyclic

Year 2 Chemistry OCR A level (9 decks)

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