Aromatic Compounds Flashcards
What at the conditions for nitration of benzene?
Concentrated HNO3
Concentrated H2SO4
50 - 55 degrees celcius
What are the equations in nitration of benzene?
HNO3 + H2SO4 = HSO4^- + NO2^+ + H2O
C6H6 + HNO3 = C6H5NO2 + H2O
HSO4^- + H^+ = H2SO4
What are the conditions for halogenation of benzene?
Bromination or chlorination
At room temperature
Requires Hogen carrier catalyst
E.g. FeBr3/AlBr3/AlCl3…
What evidence is there for structure of benzene?
Resistance to reaction - does not undergo electrophilic addition, does not react or decolourise bromine
X-ray crystallography/diffraction - bond length is between a C-C and C=C
Hydrogen enthalpy - enthalpy change is between a C-C and C=C bond
Describe the structure of benzene.
Ring of delocalised electrons
6 electrons
P orbitals overlap/merge
Above and below the plane are electron clouds
Benzene ALWAYS undergoes ELECTROPHILIC SUBSTITUTION
What are the conditions for Friedel-Crafts? Include equation.
Acylation and Alkylation (Acyl chloride and Haloalkane)
AlCl3 catal3
Room temperature
Reflux under anhydrous conditions
Equation:
AlCl3 + Cl2 = [AlCl4]^- + Cl^+
[AlCl4]^- + H^+ = AlCl3 + HCl
Describe bromination of phenol.
Electrophilic substitution
Carried out at RTP
Decolourises bromine from orange to colourless
Forms 2,4,6 - tribromophenol which is a white precipitate
Describe nitration of phenol.
Forms 2 products
2-nitrophenol and 4-nitrophenol
Dilute HNO3 at room temperature
Compare reactivity of phenol and benzene.
Phenol has lone pairs of electrons causing delocalised electrons
Causes electron density to increase
Able to polarise halogens better
Attracts more electrophiles
Note:
Bromine requires a halogen carrier catalyst to react
Alkenes have greater reactivity as they have LOCALISED electrons
How do you confirm the presence of a C=O bond?
Use 2,4 - DNP (dinitrophenylhydrazine)
Forms an orange precipitate
How do you distinguish between an aldehyde and a ketone?
Use Tollens reagent
Aldehydes form a silver mirror
Ketones do not react as they are not oxidised
Aldehydes are converted to carboxylic acid
