Aromatic Chemsitry Flashcards
What are arenes
Large family of unsaturated cyclic hydrocarbons
What makes benzene different from cyclohexatriene
- Reaction with bromine:
Substitution occurs rather than addition - Bond length:
All same bond length rather than a change between C-C and C=C - Stability:
Benzene is more stable due to stabilisation (delocalisation) energy
What is the definition of delocalisation (arenes)
The pi electrons are spread over several atoms
Describe the structure of benzene
- Symmetrical planar
- 3 sigma bonds in each C atom (with two C and one H)
- 4th electron held in p orbital
- P orbital overlaps sideways on both neighbouring p orbitals
- P orbitals fuse together and form delocalised ring above and below planar sigma bonded ring
Describe the physical properties of benzene
- Colourless liquid
- Non-polar - weak vdw
- Toxic
- Distinct aroma
- Immiscible in water
- Soluble in non polar solvents
What kind of reactions do benzene undertake
Substitution
What are the chemical properties of benzene
- Relatively stable
2. Electrophilic substitution reactions
Write the equation for mononitration
See notes
What is the electrophile in mononitration
Nitronium ion NO2+
How is the nitronium ion produced in mononitration. Write the equations
In situ
Conc sulfuric acid and conc nitric acid
It is the nitrating mixture
See notes for equations
Draw the mechanism for mononitration
See notes
What must be present for monobromination to occur and what is its general name
Iron (III) Bromide
FeBr3
A halogen carrier catalyst
Write the mechanism for monobromination
See notes
Describe the key points of monobromination
- Br2 polarised as approaches ring
- FeBr3 accepts Br- to form a Br+
- Br+ attracted to electrons in benzene
- Br+ covalently bonds to C - disrupts ring
- Electron in C-H goes back to ring - reform delocalised cloud
- FeBr4- reacts with H+ to form FeBr3 and HBr
Draw the mechanism for alkylation
See notes
