Aromatic Compounds

Question 1

conditions and reagents for the nitration of benzene

Answer 1

sulphuric acid

50°C

Question 2

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

Answer 2

might form dinitrobenzene

Question 3

what is nitrobenzene used for

Answer 3

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

Question 4

what is the electrophile in the nitration of benzene

Answer 4

NO2+

Question 5

3 steps in the nitration/halogenation of benzene

Answer 5

electrophile formation
attacks the benzene ring
regeneration of the catalyst

Question 6

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

Answer 6

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

Question 7

How is the catalyst regenerated

Answer 7

H+ ion reacts with HSO4- ion to regenerate

Question 8

what is the catalyst called in the halogenation of benzene

Answer 8

halogen carrier/Friesdel-Crafts

AlBr3

Question 9

reagents and conditions for the halogenation of benzene

Answer 9

halogen carrier

room temp and pressure

Question 10

what is alkylation of benzene

Answer 10

substitution of a h atom

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

Question 11

what is the alkylation reaction sometimes called

Answer 11

Friedel-Crafts alkylation

Question 12

what is acylation of benzene

Answer 12

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

Question 13

name the molecule when they have these groups in benzene:
chloro-
nitro-
hydroxy-
methyl-  
amino-
carboxylic acid

Answer 13

chlorobenzene
nitrobenzene
phenol
methylbenzene/toluene
phenylamine/aniline
benzenecarboxylic acid/benzoic acid

Question 14

which groups are assumed to occupy position 1

Answer 14

OH of phenol or CH3 of methylenzene

Question 15

when is benzene the substituent

Answer 15

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

Question 16

what reaction does benzene undergo

Answer 16

electrophilic substitution

Question 17

what is the purpose of alkylation

Answer 17

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

Question 18

properties of phenol

Answer 18

colourless solid at room temp- hydrogen bonds

dissociates in water

Question 19

are phenols stronger acids than alcohols?

Answer 19

yes

ethoxide ion readily accepts proton forming ethanol- positive inductive effect

Question 20

what happens when phenol reacts with aqueous alkalis

Answer 20

a salt forms

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

Question 21

why are phenols useful

Answer 21

can make phenyl esters which make polyesters

Question 22

why doesn’t phenol react with sodium carbonate solution

Answer 22

sodium carbonate isn’t a strong enough base

Question 23

2 types of phenol reactions

Answer 23

reactions of the phenol group

substitution in the aromatic ring

Question 24

what is the bromination of phenol

Answer 24

phenol + 3Br2 –> phenolBr3 + 3HBr

Question 25

what happens when there is NO2 on the aromatic ring

Answer 25

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

Question 26

phenol and 3Br2- what happens

Answer 26

decolourises and a white precipitate may be formed

Question 27

what products are formed when phenol and NaOH react

Answer 27

sodium phenoxide | no observable reaction

Question 28

what happens when phenol and NaOH react

Answer 28

sodium phenoxide and water | no observable reaction

Question 29

what happens when phenol and 3Br2 react

Answer 29

2,4,6 tribromophenol and 3HBR | decolourises bromine and white precipitate may form

Question 30

properties of benzene that are determined by the stsructure

Answer 30

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

Question 31

why does phenol react differently from benzene

Answer 31

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

Question 32

Which is most reactive Benzene Phenol/phenylamine Nitrobenzene

Answer 32

Phenol/phenylamine Benzene Nitrobenzene

Question 33

Describe the reactivity of benzene

Answer 33

Moderate temp (50oC) Catalyst Electrophilic substitution

Question 34

Describe the reactivity of nitrobenzene

Answer 34

``` 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 ```

Question 35

Describe the reactivity of phenol/phenylamine

Answer 35

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

Question 36

describe the bonding in a benzene molecule

Answer 36

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

Question 37

how does the kekule model differ from the accepted version

Answer 37

contains alternating double/single bonds

Question 38

evidence that led to reject the kekule model

Answer 38

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

Question 39

what substances and conditions used to form nitrobenzene

Answer 39

concentrated nitric and sulfuric acid | less than 50 degrees for no further substitutions

Question 40

what reacts with sodium carbonate

Answer 40

ethanoic acid would fizz | phenol doesn't as it is too much of a weak base

Question 41

what can ethanoic acid react with

Answer 41

alkalis and carbonates

Question 42

what happens with bromine and benzene vs cyclohexene and bromine

Answer 42

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