delocalised electrons are what makes benzene so stable and allow it to resist addition reactions. ...
TRANSCRIPT
BENZENEWHY ELECTROPHILIC SUBSTITUTION?
ELECTROPHILIC SUBSTITUTION…
Delocalised electrons are what makes benzene so stable and allow it to resist addition reactions.
Electron rich benzene rings are prone to attack from electrophiles
One or more of the 6 hydrogen atoms is replaced by a reacting functional group.
REACTIONS OF ARENES
THE MECHANISM E+ = electrophile. The overall equation is:
What do you think happened?
+ E+ + H+
E
GENERIC MECHANISM
STAGE 1
Positive electrophile attacks the delocalised electron ring.
A temporary intermediate is formed where the delocalisation is partially lost and the ring will join to both the original hydrogen and the new electrophile.
The overall charge of the molecule is positive so make sure you add this to your diagram.
STAGE 2
Y- comes from the system (remember that ions dissociate in solution).
It will be attracted to the H on the benzene ring and cause H to donate its electrons back to the ring.
1. NITRATION
2. FRIEDEL-CRAFTS ACYLATION
NITRONIUM ION The nitronium ion/nitryl cation is NO2
+
Firstly need to generate the nitronium ion
CONCENTRATED!!!
H2SO4 + HNO3 H2NO3+ +
HSO4-
H2NO3+ NO2
+ + H2O
MECHANISM
LOOKING AT THE BIG PICTURE…
NITROBENZENE TO PHENYL AMINE
NO2 group is reduced to NH2 group. In industry, iron is used In lab, tin is used with conc HCl as
reductant. Phenylamine is widely used in dye
industry.
WHAT IS ACYLATION?
Adding an acyl C=O group to a benzene ring….
BACKGROUND… Benzene reacts with an acyl chloride
Ethanoyl chloride is the most commonly used acyl chloride
AlCl3 catalyst
Forms a phenyl ketone and HCl.
AlCl3
GENERATING THE ELECTROPHILE…
RCOCl + AlCl3 RCO+ + AlCl4-
ELECTROPHILIC SUBSTITUTION…
Where E+ = CH3CO
EXAM QUESTIONS
Do questions 1, 4 and 5 in your books
MOREEXAM
QUESTIONS