Aromatic Chemistry
No description yet. This curated deck is ready for daily study.
Card preview (24)
What are arenes?
Hydrocarbons
What is the molecular formula of benzene?
C6H6
Is benzene saturated or unsaturated?
Unsaturated
How does benzene look like?
Hexagonal structure with a ring in the middle.
What is at each point of the hexagon of benzene?
1 carbon and 1 hydrogen
Why was the structure and bonding of benzene a puzzle for a long time?
Even though it is unsaturated, it doesn’t readily undergo addition reactions.
What does delocalisation mean?
Electrons are spread over more than two atoms.
What bond does each carbon in benzene have? How many?
3 covalent bonds. 1 to a hydrogen atom and 2 to a carbon atom.
Where does the 4th electron of each carbon atom come from?
P orbital. There are 6 of these, one on each carbon atom. It delocalises to form rings of electron density below and above the hexagon.
What do the p orbitals do?
Overlap. The electrons in them are delocalised.
What makes benzene stable?
The delocalised electrons.
How does benzene look at room temperature?
Colourless liquid
Why do compounds containing benzene have a higher melting point?
Due to the stability of the delocalised ring.
What do arenes mix with and not mix with?
Not mix with water. Mix with other hydrocarbons and non-polar solvents.
Why do compounds containing benzene have a lower boiling point?
Non-polar molecules and often can’t dissolve in water.
Describe the ring in benzene.
The ring is an area of high electron density due to delocalised bonding. It is therefore attacked by electrophiles.
What is the delocalisation energy?
The energy needed to break the ring in benzene.
What are most of the aromatic reaction mechanisms?
Electrophilic substitution.
Why do arenes burn in air? What is observed?
Smoky flames. They have a high carbon:hydrogen ratio compared with alkanes.
What is produced when arenes burn?
Unburnt carbon produces soot.
Does benzene react like an alkene even if they’re both unsaturated?
No.
Why is electrophilic substitution used rather than electrophilic addition?
Electrophilic addition would require the input of delocalisation energy to destroy the aromatic system.
What is special about the ring of high electron density?
Attracts electrophiles
How does the aromatic system get destroyed during electrophilic substitution?
A bond forms between one of the carbon atoms and the electrophile. But to do this, the carbon must use electrons from the delocalised system. This destroys the aromatic system.