Arenes Flashcards
What do arenes have to contain?
At least one benzene ring
What is the concept of resonance?
It is the phenomenon in which electrons are shared between 3 or more atoms - also known as the delocalisation of pi electrons
This results in additional stability for the species and bonds that exists
Why would resonance occur?
When 3 or more p orbitals are perpendicular to the same plane
What is the mechanism for all the reactions for arenes? Why is it the most likely?
Electrophilic Substitution.
Why electrophilic: Benzene is electron-rich; thus electrophiles are attracted to it
Why substitution: to preserve resonance
Draw the mechanism out
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What chemical reactions take place for arenes?
- Halogenation
- Nitration
- Friedel-Crafts Alkylation
- Friedel-Crafts Acylation
What is the R&C for halogenation?
- Anhydrous AlX3/FeX3, room temp
- Al or Fe, X2, room temp
What is the R&C for nitration?
Concentrated HNO3, concentrated H2SO4, 55 degrees Celcius
Draw the mechanism of halogenation?
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Draw the mechanism for nitration
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What is the Friedel-Crafts Alkylation R&C?
- anhydrous AlX3/FeX3, alkyl halide(RX), room temperature
What is the Friedel-Crafts Acylation R&C?
Anhydrous AlX3/FeX3, acyl halide, room temperature
Draw the Friedel-Crafts Alkylation mechanism
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Draw the Friedel-Crafts Acylation mechanism
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What reactions do the side chains of benzene undergo and what are the R&C?
- Halogenation via free-radical substitution (UV light, limited/excess X2(g))
- Oxidation (H2SO4(aq), KMnO4, heat under reflux)
What acids can be further oxidised to give CO2 and H2O?
Methanoic acid
Ethanedioic acid
Methylbenzene oxidises to give?
Carboxylic acid
Subsequent Cs connected to benzene gives?
RCOOH
Why do arenes have a low boiling point?
Simple covalent molecule with weak dispersion forces between molecules require little energy to overcome
What is the solubility of arenes?
Insoluble in polar aqueous solvents due to its inability to from hydrogen bonds
Soluble in non-polar organic solvents due to favourable id-id interactions
Can arenes conduct electricity?
No, because the delocalisation of electrons are not extensive
What are the activating groups? State if theyre weak or strong
Alkyl groups (weak)
O-H/R groups (strong)
N-H/R groups (strong)
What are the deactivators? State if they’re weak or strong
Halogens (weak)
NO2, CHO, COOH, CN, COOR(ester) etc. (strong)
What bonds are 2,4 directing and 3-directing?
All substituents are 2,4-directing except those with multiple bonds. Multiple bonds are 3-directing
What do activators do?
Benzene ring becomes more electron rich
What do deactivators do?
Benzene ring becomes less electron rich
How does a group activate/deactivate?
- Inductive effect due to electronegative difference
- Delocalisation/Resonance due to the lone electron pair next to the ring
