6.1.1 Aromatic Compounds: Module 6: Organic Chemistry & Analysis Chemistry OCR A A Level

What is the empirical formula of Benzene?

CH

What is the state of benzene at room temperature?

Liquid

What is the bond angle of benzene?

Bond angle = 120°

What are the 3 features of benzene that don’t support Kekule’s model?

● Benzene is resistant to addition reactions

● Enthalpy change of hydrogenation of benzene is more stable than predicted

● All the carbon bonds are same length

What technique was used to find the bond lengths of benzene?

X ray diffraction

What happens to the 4th electron in the p-orbital of each carbon atom in benzene?

It delocalises to form rings of electron density above and below the hexagon, forming rings of delocalised electron density above/below the hexagon.

How do the rings of electron density affect the stability of Benzene?

Makes benzene very stable, even though it is unsaturated (aromatic stability).

Why does benzene have a relatively high melting point?

Close packing of flat hexagonal molecules when solid.

Is benzene soluble in water? Explain why?

No because it is non polar.

Dangers of benzene - why it is not used in schools?

It is a carcinogen.

How do you name compounds containing a benzene ring?

-benzene, or phenyl- ; can designate position on ring using numbers if there is more than one substituent.

Why is benzene attacked by electrophiles?

High electron density above/below ring due to delocalised electrons.

Nitration of benzene is what type of reaction?

Electrophilic substitution reaction.

What is the catalyst in nitration of benzene?

Sulfuric acid

What type of catalyst is used for a Friedel-Crafts reaction?

A halogen carrier (e.g. AlCl 3)

Why does benzene not react directly with halogens?

The aromatic ring is too stable.

How could you use a Friedel-Crafts mechanism to add a methyl group to a benzene ring?

Use a halogenoalkane and AlCl3 to create an electrophile that can attack benzene.

What reactions can you carry out to show the weak acidity of phenol?

A neutralisation reaction with NaOH occurs but absent when you react phenol with carbonates.

What is the relative ease of electrophilic substitution of phenol compared to benzene and why?

It is easier for electrophilic substitution to occur with phenol because oxygen lone pair of electrons from the -OH group are partially delocalised into ring therefore this increases the electron density of the ring thus electrophiles are more attracted phenol.

What is the directing effect of electron donating groups OH and NH2?

They direct group to the 2 and 4 position of the ring in electrophilic substitution of aromatic compounds.

What is the directing effect of electron withdrawing group NO2?

NO2 directs atoms to the 3 position of the ring in electrophilic substitution of aromatic compounds.