Aromatic chemistry

True or false? Benzene is a planar molecule.

True.

Describe the bonding in a molecule of benzene.

Each carbon is bonded to two other carbon atoms and one hydrogen, the fourth electron of each carbon is in a p-orbital and forms a ring of delocalised electrons with the others.

True or false? All the C-C bonds in benzene are different lengths.

False. ALL THE C-C BONDS IN BENZENE ARE THE SAME LENGTH.

Why are all the C-C bonds in benzene the same length?

Due to the delocalised ring of electrons.

Draw the skeletal formula of the Kekule structure of benzene.

Draw the skeletal formula of benzene.

True or false? Benzene is more stable than (theoretical) cyclohexa-1,3,5-triene.

True.

How do the enthalpy change of hydrogenation values show benzene is more stable or cyclohexa-1,3,5-triene?

Benzene has a lower enthalpy of hydrogenation value (-208 kJ mol^-1) than cyclohexa-1,3,5-triene (-360 kJ mol^-1).

True or false? More energy is required to break the bonds in cyclohexa-1,3,5-triene than is required to break the bonds in benzene.

False. MORE ENERGY IS REQUIRED TO BREAK THE BONDS IN BENZENE (AS THEY ARE MORE STABLE) THAN IS REQUIRED TO BREAK THE BONDS IN CYCLOHEXA-1,3,5-TRIENE.

What makes benzene so stable?

The ring of delocalised electrons.

What is an aromatic compound?

A compound that contains benzene.

How do you name an aromatic compound when benzene is the functional group?

Add -benzene suffix.

How do you name an aromatic compound when benzene is not the functional group?

Add phen- prefix.

Why do aromatic compounds undergo electrophilic substitution reactions?

The electron dense ring of delocalised electrons in benzene attracts electrophiles and substitution takes place as the stable ring of delocalised electrons must be maintained (meaning no addition can take place).

Why is benzene relatively difficult to react?

Because it is such a stable molecule.

Give two general uses of aromatic compounds.

• Pharmaceuticals.

• Manufacture of dyes.

Why does the acylation of benzene make it easier to modify afterwards?

The addition of an acyl group makes benzene less stable and therefore easier to react.

What general catalyst is used in Friedel-Crafts acylation?

A halogen carrier.

Give the formula of a specific catalyst used in Friedel-Crafts acylation.

AlCl₃

Give the displayed formula equation of how an acyl chloride reacts with aluminium chloride.

Why must an AlCl₃ catalyst be used in Friedel-Crafts acylation?

To turn the acyl chloride into a stronger electrophile that will actually react with benzene.

Under what conditions does Friedel-Crafts acylation take place.

• Reflux.

• Dry ether solvent.

Draw the mechanism for Friedel-Crafts acylation.

Give two uses of nitrated benzene.

• Making dyes.

• Making explosives.

Which two reagents and what conditions must there be for the nitration of benzene?

• Concentrated nitric acid.

• Concentrated sulfuric acid.

• Heat.

Write two equations showing how the electrophile is formed for nitration of benzene.

What is the name of this ion NO₂⁺?

Nitronium ion.

Draw the reaction mechanism for the nitration of benzene.

What temperature must the nitration of benzene be to ensure that only one nitration takes place?

Bellow 55 degrees celsius.