Aromatic Compound's

Question 1

What is the molecular formula of benzene?

Answer 1

C6H6

Question 2

What is the empirical formula of benzene?

Answer 2

CH

Question 3

What term is given to any molecule that does not contain a benzene ring?

Answer 3

Aliphatic

Question 4

What do aromatic compounds contain?

Answer 4

A benzene ring

Question 5

How many delocalised electrons does benzene contain?

Answer 5

6

Question 6

What are some problems with the Kekules structure?

Answer 6

Enthalpies of hydrogenation
Reactivity
C-C bond lengths

Question 7

Benzene does not undergo electrophilic addition reactions with halogens at room temperature like alkenes so what does it undergo?

Answer 7

Benzene will only react with halogens if a catalyst is present. It then undergoes an electrophilic substitution reaction with halogens.

Question 8

Describe bonding in benzene

Answer 8

Each carbon has 4 outer electrons; one is used to bond to a hydrogen; 2 are used to bond to adjacent carbons; the remaining electron from each carbon form a cloud of delocalised electrons above and below the plane of the ring.

Question 9

Delocalisation gives rise to extra stability called what?

Answer 9

Delocalisation energy

Question 10

If alkyl groups with less than 7 carbons, nitro groups and halogens are attached directly to a benzene ring, they are what?

Answer 10

Prefixes to benzene
- put in alphabetical order
- use di, tri and number

Question 11

If a benzene ring is attached to an alkyl group with a functional group or an alkyl group with 7 or more carbon atoms what prefix is used instead of benzene?

Answer 11

Phenyl

Question 12

What is the prefix/name when there’s a OH attached directly to ring?

Answer 12

Phenol

Question 13

What is the prefix/name when there’s a NH2 attached directly to ring?

Answer 13

Phenylamine

Question 14

What is the prefix/name when there’s a COOH attached directly to ring?

Answer 14

Benzoic acid

Question 15

What is the prefix/name when there’s a CHO attached directly to ring?

Answer 15

Benzaldehyde

Question 16

When are prefixes for NH2 (amino) and OH (hydroxyl) used?

Answer 16

When COOH or CHO take priority, or there is more than one amino or hydroxyl group

Question 17

What are the reactions and conditions for a chlorination reaction?

Answer 17

Cl2 with AlCl3 catalyst

Question 18

What are the reactions and conditions for a bromination reaction?

Answer 18

Br2 with AlBr3 catalyst

Question 19

What are the reactions and conditions for a nitration reaction?

Answer 19

Concentrated nitric acid, concentrated sulfuric acid, heat under reflux at 50 degrees for mononitration.

Question 20

What are the reactions and conditions for an alkylation reaction?

Answer 20

Alkyl chloride(haloalkane) with AlCl3 catalyst

Question 21

What are the reactions and conditions for an acylation reaction?

Answer 21

Acyl chloride with AlCl3 catalyst

Question 22

What does the donation of a proton from the OH group enable?

Answer 22

Phenol and carboxylic acids

Question 23

Why do aromatic compounds do electrophilic substitution not addition?

Answer 23

Substituting ensures stable pi ring is re-formed

Question 24

Describe the Kekule model of benzene

Answer 24

Alternating single and double C-C bonds

Question 25

How does a pi bond form?

Answer 25

Sideways overlap of adjacent p orbitals above and below the bonding atoms

Question 26

What is the electrophile in the bromination of benzene?

Answer 26

Br+, bromonium ion

Question 27

What type of mechanism do alkenes tend to react in?

Answer 27

Electrophilic addition

Question 28

What type of acid is phenol and what does it react with?

Answer 28

A weak acid Reactive metals - Na and bases - NaOH

Question 29

What type of acid is a carboxylic acid and what does it react with?

Answer 29

Weak acid Reactive metals, bases and metal carbonates

Question 30

How does phenol react as a weak acid?

Answer 30

The OH group on phenol donates a proton to water when in aqueous solution. This occurs due to delocalisation of the negative charge of the O- around the delocalised pi bond system of the benzene ring. This makes the phenoxy ion more stable.

Question 31

What simple chemical test could you do to distinguish between phenol and a carboxylic acid?

Answer 31

Metal carbonate test as phenol will not react with carbonates as it is a very weak acid and carboxylic acids do react with carbonates - effervescence will be observed.

Question 32

Whats the difference between an acid and a base?

Answer 32

An acid is a proton donor and a base is a proton acceptor.

Question 33

What is amine?

Answer 33

A weak base due to the lone pair on the nitrogen atom.

Question 34

How does increasing the electron density affect the amine as a base?

Answer 34

The greater the electron density on the N, the easier it can pick up protons and the amine is a stronger base. This is affected by the groups attached to the nitrogen

Question 35

Describe the reaction of phenylamine as a very weak base.

Answer 35

The lone pair on the N is delocalised into the pi bond system, the electron density on N is lowered, the lone pair is less effective at accepting a proton

Question 36

Describe the reaction of methylamine as a weak base.

Answer 36

Alkyl groups donate electrons to N, electron density on N is increased and the lone pair is more effective at accepting a proton

Question 37

When amines dissolve in water what do they produce?

Answer 37

Weak alkaline solutions

Question 38

When amines react with acids what do they produce?

Answer 38

Salts

Question 39

To reform the amine from its salt what do you add?

Answer 39

Aqueous sodium hydroxide as NaOH is a stronger base than the amine and accepts a proton from the salt.

Question 40

Does phenol undergo electrophilic substitution much more easily than benzene?

Answer 40

Yes

Question 41

Why does phenol undergo electrophilic substitution much more easily than benzene?

Answer 41

- phenol has two lone pairs on the oxygen of the phenol group - one of these pairs of electrons is delocalised around the ring - this increases the electron density in the pi bond system - the electrophile is attracted more easily to the pi bond system - a non-polar electrophile can be polarised without the need for a halogen carrier

Question 42

What happens when bromine water is added to a solution of phenol in water?

Answer 42

The bromine water is decolourised and a white precipitate forms which smells of antiseptic.

Question 43

Compare the addition of bromine water to phenol and an alkene?

Answer 43

Bromine water is normally used as a test for a c=c double bond in an alkene. The important difference with phenol is the formation of a white precipitate as well as the bromine water being delocalised.

Question 44

What happens when you react phenol with dilute nitric acid?

Answer 44

Phenol reacts with dilute nitric acid at room temperature to give a mixture of 2-nitrophenol an 4-nitrophenol. This is a mono-nitration.

Question 45

What are the conditions needed to get from nitrobenzene to amino-benzene?

Answer 45

Sn (Tin) Conc HCl Heat under reflux

Question 46

What are the conditions needed to get from nitrobenzene to amino-benzene?

Answer 46

Sn (Tin) Conc HCl Heat under reflux