Chapter 25 - Aromatic compounds Flashcards

1
Q

Formula of benzene

A

C6H6

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What type of hydrocarbon is benzene?

A

Aromatic - it is an arene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is Kekule’s model of benzene?

A

The six carbon ring is joined by alternating single and double bonds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the three pieces of evidence to disprove Kekule’s model?

A

Benzene’s lack of reactivity
The length of the c-c bonds
Hydrogenation enthalpy of benzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Why does benzene’s lack of reactivity disprove Kekule’s model?

A

Benzene doesn’t undergo addition reactions or decolourise bromine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why does the length of benzene’s c-c bonds disprove kekule’s model?

A

The c-c bond is between the length of the single and double bond

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Why does the hydrogenation enthalpy of benzene disprove kekule’s model?

A

Its expected enthalpy would be triple the enthalpy of cyclohexene but it doesn’t

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the delocalised model of benzene?

A

Each carbon uses three of its four electrons to bond to 2 x C and 1 x H
The overlapping of unused p-orbitals creates a system of pi-bonds which spread over the six atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

When will the prefix ‘phenol’ be used?

A

When the alkyl group attached to the benzene has more than 7 carbon atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What happens when benzene is nitrated?

A

One of the hydrogen atoms on the benzene ring is replaced with a NO2 group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is used to catalyse the reaction between benzene and a nitrate group?

A

Sulfuric acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is the nitronium ion produced?

A

Nitric acid reacts with sulfuric acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What must be present for a halogen to react with benzene?

A

A halogen carrier, e.g. AlCl3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How does benzene reacts with alkyl groups?

A

A hydrogen atom in the benzene ring is replaced by an alkyl group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Conditions needed for alkylation?

A

React benzene with a haloalkane in the presence of a halogen carrier

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Why is alkylation useful?

A

Increases the length of the carbon chain

17
Q

What is an acylation reaction?

A

When benzene reacts with an acyl chloride in the presence of an AlCl3 catalyst

18
Q

What is produced when benzene is acylated?

A

An aromatic ketone

19
Q

Why won’t benzene react with bromine unless a halogen carrier is present?

A

Benzene has delocalised electrons above and below the c-c ring
Lower electron density
When a non-polar molecule like benzene approaches, this means there are insufficient electrons to polarise the bromine

20
Q

What is a phenol?

A

An OH group bonded to a benzene ring

21
Q

What is the difference between an alcohol and a phenol?

A

An alcohol involves a OH group bonded to a carbon side chain, not to benzene itself

22
Q

Why is phenol less soluble than alcohol?

A

The benzene ring is non-polar

23
Q

Why is phenol a weak acid?

A

Phenol partially dissociates when dissolved in water

24
Q

Will ethanol react with sodium hydroxide or sodium carbonate?

25
Will phenols and carboxylic acids react with NaOH?
Yes
26
Will carboxylic acids react with sodium carbonate?
Yes
27
What happens when phenol is brominated?
Bromine is added to the benzene ring - no halogen carrier needed
28
Why do halogens and nitric acid react more readily with phenol than benzene?
A lone pair of electrons is donated from the oxygen atom to the pi-system This increases the electron density so it can attract electrophiles more readily
29
What is activation?
The aromatic ring reacts more readily with electrophiles
30
What is deactivation?
The aromatic ring reacts less readily with electrophiles
31
What type of directing is -NH2?
2 or 4
32
What type of directing is -NO2?
3