6A Arenes

Benzene molecular formula

What do aliphatic, aromatic, alicyclic, saturated and unsaturated mean

Benzene molecular formula

C6H6

What does the structure of delocalised benzene and kekule benzene look like

Evidence for the delocalised structure of benzene

Each C-C bond length is the same

Benzene reactivity is different to an alkene, benzene cannot do electrophillic addition like alkenes

Less exothermic enthalpy change of hydrogenation than expected, this means more energy was needed to break C=C bonds in benzene than expected (more ends than it should be)

How to form structure of benzene

Adjacent p orbitals overlap sideways to form pi bonds, the pi bonds spread over above and below the plane, the electrons are therefore delocalised.

What are similarities and differences between kekule and delocalised structure of benzene

Similarities:

Both models involve overlap of p orbitals

Both models suggest there is n - electron density above and below the plane of the ring

Differences:

Kekule model suggests alternating pi bonds but delocalised model suggests delocalised pi ring system.

How do you name aromatics using prefixes

How do you name aromatics with suffix naming

What is a phenol

An OH group on a benzene

What endings are these molecules

NO2

NH2

NO2 = nitro

NH2 = amino

What is the suffix for RCOCl groups (Acyl chlorides)

- oyl chloride eg: butanoyl chloride

What are the 5 reactions of benzene

Nitration= reagent = HNO3 Catalyst = H2SO4

Chlorination reagent = Cl2 Catalyst = AlCl3

Bromination reagent = Br2 Catalyst = AlBr3

Acylation reagent = RCOCl (R = anything) Catalyst = AlCl3

Akylation reagent = RCl (R = anything) Catalyst = AlCl3

What product does chlorination produce

Methyl benzene

What product does Acylation produce

Phenyl ketone

What product does nitration form

What are the steps for the reactions of Benzene

Eg: bromination in this case but

The reactant reacts with the catalyst to form a charged ion and negative product

Benzene reacts with the charged ion to form arene and h+ ion

Catalyst is reformed from H+ reacting with negative product

Cancel things that come up on both sides of equation to get overall equation

Nitration reaction with benzene

What is the Acylation reaction with benzene

What is the alkylation reaction with benzene

Electrophillic substitution of benzene

First you have an electrophile with a curly arrow coming from circumference of the circle

A bond is then formed with electrophile and carbon with hydrogen originally being there

A horseshoe with cation is in the middle with a curly arrow being drawn from hydrogen to the centre. This adds 2 electrons on it so benzene can be re - established

H becomes H+ as it has lost an electron and E (electrophile) replaces the H as a substitution reaction

Electrophillic substitution with an actual electrophile

What are phenols

Contain a hydroxyl group (-o-h) bonded directly onto benzene ring

1 OH group is phenol

More than 1 use the suffix ol

Use of phenol

It is an antiseptic

What is the appearance of phenol?

What is the solubility of phenol?

A pink solid

It can dissolve because of the hydrogen bonds. However, it is sparingly soluble as most of the molecule is non polar

What type of acid is phenol

Weak acid, they react with metals and strong bases

They don’t react with carbonates as they are weak bases

Explain the reactivity of phenol compared to benzene/ Why is phenol much more reactive than benzene

Benzene has pi rings above and below plane of rings

Phenol has pi rings above and below with an OH

lone pair on O of OH is delocalised into the ring

This makes ring more electron rich

Therefore the ring is able to induced dipoles into electrophile

What can phenols react without

A catalyst and at room temperature and pressure

Describe the acidity of phenols

Electrons in OH bond are delocalised into benzene ring

This makes OH bond weaker

This means H+ is formed more easily

What are the Reactions of phenols

•Phenol reacts with water (aq) to form phenoxide ion and H+ ion

•No reaction occurs between phenol and carbonate

•Phenol reacts with sodium hydroxide (NAOH) to form sodium phenoxide and water.

To turn sodium phenoxide back to phenol needs to be a strong acid eg: HCl or H2SO4

•phenol reacts with 3 molecules of bromine water (3Br2 aq) to form 2,4,6 tribromophenol and 3 molecules of hydrogen bromide.

•Phenol can react with nitric acid (HNO3 (aq) to form

a mixture of 2 nitrophenol and 4 nitrophenol with water and a product too.

When phenol reacts with the 3 molecules of bromine (3Br2) (aq) what observations are found

Bromine is decolourised

A white precipitate of 2,4,6 tribromophenol is formed

In directing effects if the molecule is a phenol or amine group on it, what director is it

2,4,6

Meaning the molecule it reacts with binds to the 2nd,4th, and 6th position

I’m directing effects if the molecule is a nitro what director is it

3 director

Meaning the molecule it reacts with bonds on to the third position

Example of directing

Out of alkenes, arenes and alkanes which is the most to least reactive with electrophiles and why?

Alkene is most = can polarise electrophiles without a catalyst

Arenes 2nd most = a catalyst is needed to ionise elcetrophiles, activated Arenes don’t need a catalyst

alkane least reactive = do not undergo Electrophillic attack so no electron density

However, benzene is less reactive than cyclohexane

How to work out theoretical mass or actual mass in percentage yield question when given percentage yield

If trying to find actual mass it’s 100/ percentage yield

If trying to find theoretical yield it’s percentage yield /100

How to answer this type of question

Say which ones have the same carbon environments

Which ones have different carbon environments

Whether they can be distinguished (one that has different environments can be distinguished)