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Chemistry Dawes Y13 > Aromatic Compounds > Flashcards

Aromatic Compounds Flashcards

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1
Q

conditions and reagents for the nitration of benzene

A

sulphuric acid

50°C

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2
Q

what happens if the temperature in the nitration of benzene rises above 50°C

A

might form dinitrobenzene

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3
Q

what is nitrobenzene used for

A

a starting material in the preparation of dyes, pharmaceuticals, and pesticides

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4
Q

what is the electrophile in the nitration of benzene

A

NO2+

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5
Q

3 steps in the nitration/halogenation of benzene

A

electrophile formation
attacks the benzene ring
regeneration of the catalyst

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6
Q

how does the electrophile attack the benzene ring in the nitration of benzene

A

NO2+ accepts a pair of electrons from the benzene ring to form a dative covalent bond.
The organic intermediate formed is unstable, and breaks down to form nitrobenzene and a H+ ion
A stable benzene ring is reformed

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7
Q

How is the catalyst regenerated

A

H+ ion reacts with HSO4- ion to regenerate

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8
Q

what is the catalyst called in the halogenation of benzene

A

halogen carrier/Friesdel-Crafts

AlBr3

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9
Q

reagents and conditions for the halogenation of benzene

A

halogen carrier

room temp and pressure

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10
Q

what is alkylation of benzene

A

substitution of a h atom

haloalkane and benzene react in the presence of AlCl3 which acts as a halogen carrier

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11
Q

what is the alkylation reaction sometimes called

A

Friedel-Crafts alkylation

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12
Q

what is acylation of benzene

A

benzene reacts with acyl chloride in the presence of AlCl3 catalyst
forms a aromatic ketone
electrophilic substitution

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13
Q 
name the molecule when they have these groups in benzene:
chloro-
nitro-
hydroxy-
methyl-  
amino-
carboxylic acid
A 
chlorobenzene
nitrobenzene
phenol
methylbenzene/toluene
phenylamine/aniline
benzenecarboxylic acid/benzoic acid
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14
Q

which groups are assumed to occupy position 1

A

OH of phenol or CH3 of methylenzene

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15
Q

when is benzene the substituent

A

when it is attached to an alkyl chain with a 7+ carbons= phenyl

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16
Q

what reaction does benzene undergo

A

electrophilic substitution

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17
Q

what is the purpose of alkylation

A

to increase the number of carbon atoms in a compound by forming C-C bonds

18
Q

properties of phenol

A

colourless solid at room temp- hydrogen bonds

dissociates in water

19
Q

are phenols stronger acids than alcohols?

A

yes

ethoxide ion readily accepts proton forming ethanol- positive inductive effect

20
Q

what happens when phenol reacts with aqueous alkalis

A

a salt forms

as phenol is a weak acid, it will react readily with the strong alkali sodium hydroxide to form sodium phenoxide

21
Q

why are phenols useful

A

can make phenyl esters which make polyesters

22
Q

why doesn’t phenol react with sodium carbonate solution

A

sodium carbonate isn’t a strong enough base

23
Q

2 types of phenol reactions

A

reactions of the phenol group

substitution in the aromatic ring

24
Q

what is the bromination of phenol

A

phenol + 3Br2 –> phenolBr3 + 3HBr

25
Q

what happens when there is NO2 on the aromatic ring

A

the ring reacts less readily with electrophiles, so requires a halogen carrier and high temp as it reacts slower than benzene

26
Q

phenol and 3Br2- what happens

A

decolourises and a white precipitate may be formed

27
Q

what products are formed when phenol and NaOH react

A

sodium phenoxide

no observable reaction

28
Q

what happens when phenol and NaOH react

A

sodium phenoxide and water

no observable reaction

29
Q

what happens when phenol and 3Br2 react

A

2,4,6 tribromophenol and 3HBR

decolourises bromine and white precipitate may form

30
Q

properties of benzene that are determined by the stsructure

A 
all carbon-carbon bonds same length
can be attacked by electrophile due to density
undergoes substitution not addition
is planar
stable structure
31
Q

why does phenol react differently from benzene

A

electrons from one of oxygens p-orbitals overlap with the benzene rings delocalised system, increasing its electron density
this makes the ring more likely to be attacked by electrophiles

32
Q

Which is most reactive
Benzene
Phenol/phenylamine
Nitrobenzene

A

Phenol/phenylamine
Benzene
Nitrobenzene

33
Q

Describe the reactivity of benzene

A

Moderate temp (50oC)
Catalyst
Electrophilic substitution

34
Q

Describe the reactivity of nitrobenzene

A 
Deactivating 
3 directing 
Less readily reacts with electrophiles
Strong electronegativity of nitrogen so decreases availability of electrons so less dense 
High temp 
Halogen carrier needed
35
Q

Describe the reactivity of phenol/phenylamine

A

Activating
2,4,6 directing
Lone pairs on OH/NH2 interact with ring making it more electron dense
Increased availability of electrons from lone pairs

36
Q

describe the bonding in a benzene molecule

A

3 electrons from each C is used to form sigma bonds to 2C and H
delocalised system of electrons
pi bonds above and below plane of C atoms
p-orbital overlaps with electrons from adjacent C atoms

37
Q

how does the kekule model differ from the accepted version

A

contains alternating double/single bonds

38
Q

evidence that led to reject the kekule model

A

benzene less reactive than predicted- halogenation of benzene
the enthalpy change of benzene is lower than expected
model doesn’t show that all C-C bonds are the same length

39
Q

what substances and conditions used to form nitrobenzene

A

concentrated nitric and sulfuric acid

less than 50 degrees for no further substitutions

40
Q

what reacts with sodium carbonate

A

ethanoic acid would fizz

phenol doesn’t as it is too much of a weak base

41
Q

what can ethanoic acid react with

A

alkalis and carbonates

42
Q

what happens with bromine and benzene vs cyclohexene and bromine

A

benzene and bromine- C-H bond breaks and electrons donated to ring
stable delocalised structure regenerated
benzene and cyclohexene- carboation unstable

Chemistry Dawes Y13 (4 decks)

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