Chapter 25 - Aromatic compounds Flashcards

1
Q

What is the molecular formula of benzene?

A

C6H6

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2
Q

What is the Kekulé model?

A

Carbon atoms joined together with alternating double and single bonds

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3
Q

What are the three pieces of evidence that disproves the kekulé model?

A

Benzene does not take place in electrophilic addition reactions which alkenes do, all the bond lengths are between the length of single and double bonds and the enthalpy change of hydration of benzene is less negative than three double bonds.

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4
Q

Describe the structure of benzene?

A

Each carbon atom has a delocalised electron in a p orbital forming a ring of electron density and a system of pi-bonds

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5
Q

What groups are prefixes to benzene?

A

alkyl groups, halogens and nitro groups

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6
Q

When is the prefix phenyl used when naming benzene?

A

When the benzene ring is attached to an alkyl chain with a functional group or contains seven or more carbons

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7
Q

What does benzene and nitric acid form?

A

nitrobenzene

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8
Q

What catalyst and heat is used in forming nitrobenzene?

A

sulphuric acid at 50 degrees celsius

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9
Q

what type of reaction mechanism is the nitration of benzene?

A

electrophilic substitution

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10
Q

what happens if the temperature in the reaction between nitric acid and benzene is heated above 50°C?

A

further substitution reactions may occur leading to the production of dinitrobenzene

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11
Q

what is the electrophile in the nitration of benzene?

A

a nitronium ion

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12
Q

what is needed for the halogens react with benzene?

A

A halogen carrier

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13
Q

what is the reaction mechanism for the reaction between benzene and halogens?

A

electrophilic substitution

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14
Q

what would happen during bromination of the benzene ring?

A

One of the hydrogen atoms on the benzene ring is replaced by bromine atom

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15
Q

what is the alkylation of benzene?

A

The substitution of hydrogen atom in the benzene ring by an alkyl group

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16
Q

what is formed when benzene reacts with an acyl chloride in the presence of a aluminium chloride catalyst?

A

an aromatic ketone

17
Q

what is the reaction mechanism for when alkenes decolourise bromine?

A

electrophilic addition

18
Q

why does benzene not react with bromine unless a halogen carrier catalyst is present unlike alkenes?

A

when a nonpolar molecule approaches the benzene ring there is insufficient electron density around any two carbon atoms to polarise the bromine molecule

19
Q

what are phenols?

A

A type of organic chemical containing a hydroxyl functional group

20
Q

why is phenol less soluble in water than alcohols?

A

due to the presence of the nonpolar benzene ring

21
Q

what happens to phenol in water?

A

it partially dissociates forming the phenoxide ion and a proton

22
Q

how do we know that phenol is more acidic than alcohols but less acidic than carboxylic acids?

A

ethanol does not react with strong or weak bases, phenol and carboxylic acids react with strong bases but only carboxylic acids can react with weak bases

23
Q

A reaction with what can be used to distinguish between a phenol and a carboxylic acid

A

Sodium carbonate

24
Q

Phenol reacts with sodium hydroxide to form what products and what kind of reaction

A

Salt, sodium phenoxide and water in a neutralisation reaction

25
Q

The bromination of phenol and the nitration of phenol examples of what kind of reaction

A

Electrophilic substitution

26
Q

why does bromine and nitric acid react more readily with phenol than they do with benzene?

A

The lone power of electrons from the oxygen of the OH group are donated into the pi system of phenol so the electron density of the benzene ring in phenol is increased which attracts electrophiles more strongly

27
Q

what is the name of a second substitution?

A

Disubstitution

28
Q

what does bromine require to react with benzene?

A

A halogen carrier

29
Q

does bromine require a hydrogen carrier to react with phenylamine?

A

No, it reacts rapidly

30
Q

why does nitrobenzene react slowly with bromine and requires a hydrogen carrier and a high temperature?

A

The benzene ring in nitrobenzene is less susceptible to electrophilic substitution than benzene itself

31
Q

what does the NH2 group do to the ring as a result of the aromatic ring reacting more readily with electro files?

A

It activates it

32
Q

What does the N2 group do to the aromatic ring as the ring reacts less readily with electrophiles?

A

It deactivates it

33
Q

What positions does the NH2 group direct the second substituent?

A

two and four

34
Q

what position does the NO2 group direct the second substituent?

A

three

35
Q

what position does the OH group direct the second substituent?

A

Two and four

36
Q

are two and four directing groups activating or deactivating groups?

A

Activating

37
Q

what group of elements are two and four directing groups but not activating groups?

A

The halogens

38
Q

Are three directing groups deactivating or activating?

A

Deactivating