Chapter 25 - Aromatic compounds

Question 1

What is the molecular formula of benzene?

Answer 1

C6H6

Question 2

What is the Kekulé model?

Answer 2

Carbon atoms joined together with alternating double and single bonds

Question 3

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

Answer 3

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.

Question 4

Describe the structure of benzene?

Answer 4

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

Question 5

What groups are prefixes to benzene?

Answer 5

alkyl groups, halogens and nitro groups

Question 6

When is the prefix phenyl used when naming benzene?

Answer 6

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

Question 7

What does benzene and nitric acid form?

Answer 7

nitrobenzene

Question 8

What catalyst and heat is used in forming nitrobenzene?

Answer 8

sulphuric acid at 50 degrees celsius

Question 9

what type of reaction mechanism is the nitration of benzene?

Answer 9

electrophilic substitution

Question 10

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

Answer 10

further substitution reactions may occur leading to the production of dinitrobenzene

Question 11

what is the electrophile in the nitration of benzene?

Answer 11

a nitronium ion

Question 12

what is needed for the halogens react with benzene?

Answer 12

A halogen carrier

Question 13

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

Answer 13

electrophilic substitution

Question 14

what would happen during bromination of the benzene ring?

Answer 14

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

Question 15

what is the alkylation of benzene?

Answer 15

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

Question 16

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

Answer 16

an aromatic ketone

Question 17

what is the reaction mechanism for when alkenes decolourise bromine?

Answer 17

electrophilic addition

Question 18

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

Answer 18

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

Question 19

what are phenols?

Answer 19

A type of organic chemical containing a hydroxyl functional group

Question 20

why is phenol less soluble in water than alcohols?

Answer 20

due to the presence of the nonpolar benzene ring

Question 21

what happens to phenol in water?

Answer 21

it partially dissociates forming the phenoxide ion and a proton

Question 22

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

Answer 22

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

Question 23

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

Answer 23

Sodium carbonate

Question 24

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

Answer 24

Salt, sodium phenoxide and water in a neutralisation reaction

Question 25

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

Answer 25

Electrophilic substitution

Question 26

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

Answer 26

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

Question 27

what is the name of a second substitution?

Answer 27

Disubstitution

Question 28

what does bromine require to react with benzene?

Answer 28

A halogen carrier

Question 29

does bromine require a hydrogen carrier to react with phenylamine?

Answer 29

No, it reacts rapidly

Question 30

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

Answer 30

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

Question 31

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

Answer 31

It activates it

Question 32

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

Answer 32

It deactivates it

Question 33

What positions does the NH2 group direct the second substituent?

Answer 33

two and four

Question 34

what position does the NO2 group direct the second substituent?

Answer 34

three

Question 35

what position does the OH group direct the second substituent?

Answer 35

Two and four

Question 36

are two and four directing groups activating or deactivating groups?

Answer 36

Activating

Question 37

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

Answer 37

The halogens

Question 38

Are three directing groups deactivating or activating?

Answer 38

Deactivating