Aromatic Chemistry Chp25 Flashcards
What did the bonds of benzene turn out to be?
Turned out to be the same length; 0.140nm, a perfect hexagon
Why is benzene more stable than an alkene?
The lone electrons in the p orbitals overlap above and below the ring to form pi bonds, the pi bonds are then delocalised so charge is spread making it more stable therefore more energy is required to break bonds in benzene.
Why doesn’t benzene undergo electrophilic addition?
This would disrupt the stable ring of electrons.
How is acylation useful?
Adding a acyl group weakens benzene structure and makes it easier to modify further to make useful products.
Why are halogen carriers used?
Halogen carrier act a catalyst (AlCl3) which will produce a much stronger electrophile with a stronger positive charge so it can pass through the benzene ring.
Conditions reagents and catalysts for Nitration
Conditions - 50•c
Reagents - Conc HNO3/ Conc H2SO4
Catalyst - conc H2SO4
Formation of electrophile for nitration (equation)
HNO3 reacts with H2SO4 and makes the electrophile and water.
HNO3 + H2SO4 -> (NO2+) + H2O + (HSO4-)
Conditions, reagents and catalyst for Halogenation.
Reagents - FeBr/AlBr3 (conditions)
Conditions - Room temperature
Formation of electrophile Halogenation (equation)
Br2 + FeBr3 —> FeBr4- + Br+
Friedel Crafts Alkylation
C2H5Cl + AlCl3 —> C2H5 + HCl
Friedel Crafts Acylation
C2H3ClO + AlCl3 —> COCH3 + HCl
Describe the bonding in a benzene molecule
Each carbon atom is bonded to two other carbon atoms and one hydrogen. The 4th bond pair of electrons of each carbon atom is delocalised creating a ring of delocalised electrons above and below the plane.
How is the kekulé model different from the accepted model?
Ring of carbon atom joined by alternate single and double bonds.
Reactivity of phenol
Phenol is more reactive than benzene, phenol reacts instantly with bromine at room temp to form a white precipitate.
How does the aromatic ring become activated?
The lone pair of electrons on the oxygen atom in the phenol group delocalised into benzene ring, lone pair becomes part of the delocalised ring increasing the electron density in the ring, this makes make aromatic ring more nucleophilic and more susceptible.
