Aromaticity Flashcards
What is the molecular formula of benzene?
C6H6
Describe the bonding in benzene
It has a 6 carbon atom which each form a single covalent bond to the carbon next to them and a hydrogen atom.
This means there is 1 unpaired electron in the outer p-orbital. These combine to form a delocalised ring of electrons
Describe the delocalised electron system of benzene in terms of bonds
The p orbitals overlap, this produces a pi bond system. These electrons are spread over the whole ring so described as being delocalised.
What are the general names of compounds containing a benzene ring?
Aromatic compound / arenes
Why cant electrophilic addition occur in benzene?
electrophilic addition would break up the delocalised ring, which is very stable.
What are the 3 electrophilic substitution mechanisms for benzene?
Halogenation
nitration
Freidal Crafts Acylation
How is the acyl chloride made to use in friedal-crafts acylation?
It is reacted with AlCl3, it accepts a lone pair of electrons from acyl chloride. This increases polarisation of the acyl chloride and forms a carbocation.
Making a much stronger electrophie.
What conditions are needed for freidal-crafts acylation ?
Heated under reflux in non- aqueous solvent
Why are electrophiles attracted to benzene?
They are attracted to the areas of high electron density
Name the catalyst for nitration
Sulphuric acid
What is the mechanism to make the electrophile for nitration?
HNO3 + H2SO4 = NO2+ + H30+ 2HSO4-
How do you ensure only 1 NO2 group is added in nitration?
The temperature must be below 55 degrees
What conditions and catalyst are needed for halogenation?
Room temp
Halogen carrier - FeBr3 or AlBr3
Formation of electrophile for halogenation
Br2 + FeBr3 = Br+ + FeBr4-
How is the catalyst reformed in Halogenation?
FeBr4- + H = FeBr3 + HBr
