Aromatic Compounds 6.1.1 Flashcards
what is Benzene?
A hydrocarbon with a cyclical structure.
C6H6
What was the Kekule Structure?
Plannar cyclical structure
Alternating C-C and C=C bonds
H’s pointing outwards
What are problems with the Kekule Structure?
The carbon carbon bonds were all the same length in benzene, but C-C and C=C bonds are different lengths.
Benzene doesn’t behave like an alkene, doesn’t easily undergo addition reactions.
Benzenes hydrogenation value is less exothermic than expected, showing benzene is more stable than expected.
What is the Delocalised model of Benzene?
It has benzene as a hexgonal carbon structure, with the P orbitals of the carbons being delocalised in rings above and below the carbons. 3 Electrons above, 3 electrons below.
What is the resonance hybrid model of benzene?
It is the kekule model however the double bonds and single bonds switch at such high frequency they appear as the delocalised model.
What is Electrophilic Substitution?
When a Powerful electrophile switches places with a atom or branch within the molecule.
eg. Nitration of Benzene or Halogenation or Friedel Craft
What are the Reagents and Conditions for the Nitration of Benzene?
Reagents: Concentrated Nitric Acid Concentrated Sulphuric Acid (catalyst) Conditions: Reflux 55°C
What is the Nitronium ion?
NO2+
It is a Powerful electrophile used for the nitration of benzene.
What is the equation for the production of Nitronium Ion?
H2SO4 + HNO3 → HSO4- + NO2+ + H2O
What is the Equation for the Nitration of Benzene?
C6H6 + HNO3 → C6H5NO2 + H2O
How is H2SO4 a Catalyst in the Nitration of Benzene?
H2SO4 becomes HSO4- , and the second H reacts with HNO3 to becom Water and NO2+.
NO2+ and a H in the benzene switch place, the H+ from the Benzene reacts with HSO4- to produce H2SO4.
What are uses of the Nitration of Benzene?
Production of Dyes and explosives.
What are the Reagents and Conditions required for Halogenation of Benzene?
Reagents: Chlorine Halogen Carrier (catalyst) Conditions: Reflux in presence of a halogen carrier.
Why is a Halogen Carrier needed for Halogenation of Benzene?
Because Halogen moleules are non-polar.
The Halogen carrier polarises the molecule.
What is the Equation of the Halogen and the Halogen Carrier?
Cl2 + FeCl3 (Or AlCl3) → FeCl4- (Or AlCl4-) + Cl-
What is the Equation for the Halogenation of Benzene?
C6H6 + Cl2 → C6H6Cl + HCl
Where do the Curly arrows go in Electrophilic substitution of Benzene?
Step one)
From Ring to Electrophile
Step two)
From Hydrogen (the one on the same carbon as the electrophile) to +
What is a Friedel Craft Reaction?
When a C-C bond is formed with a Benzene.
What are the two types of Friedel Craft Reactions?
Acylation:
When an acyl group is substituted in to a benzene ring.
Alkylation:
When a alkyl group is substituted in to a Benzene ring.
What are the Reagents and Conditions of Alkylation?
Reagents: Alkyl Chloride (RCl) Halogen Carrier (Catalyst) Conidtions: Anhydrous (dry)
What is the Equation for Alkylation?
C6H6 + RCl → C6H5R + HCl
eg(C6H6 + CH3Cl → C6H5CH3 + HCl)
What are the Reagents and conditions for Acylation?
Reagents: Acyl Chloride Halogen Carrier (catalyst) Conditions: Anhydrous
What is an Alky Group?
An Alkane that is missing a Hydrogen.
eg CH3+
What is a Acyl Group?
An Alkyl group containing a C=O bond.
eg CH3CO+
What is the Equation for Acylation?
C6H6 + RCOCl → C6H5COCl + HCl
eg(C6H6 + CHCOCl → C6H5COCL + HCl)
What is the Equation for the creation of an Electrophile used in Friedel Craft Reactions?
Alkyl: Catalyst + Alkyl Chloride → Alkyl + Catalyst Chloride
eg(FeCl3 +CH3Cl → CH3+ + FeCl4-)
Acyl: Catalyst + Acyl Chloride → Acyl + Catalyst Chloride
eg(AlCl3 + CH3COCl → CH3CO+ + AlCl4-)
What is a Phenol?
A Benzene Ring with an OH group instead of onme of the H’s.
It is an almost colourless crystalline solid.
They are very weak acids, can react with metals and hydroxides but not carbonates.
C6H5OH
How does Phenol react with Sodium Hydroxide?
C6H6OH (aq) + NaOh (aq) → C6H5O-Na+ (aq) + H2O
How does Phenol react with Sodium?
2(C6H5OH) (s) + 2Na (s) → 2(C6H5O-Na+) (s) + H2 (g)
What is the Activation of a Benzene Ring?
When a species attaches to a Benzene ring its lone pair can merge with the delocalised rings of the Benzene.
Making the rings more negative(activated), therefore more reactive with electrophiles.
What is the Bromination of Phenol?
When Phenol reacts with Bromine water.
The reaction does not require a Catalyst or Halogen Carrier.
C6H5OH + 3Br2 → C6H5OHBr3 (2,4,6-Tribromophenol) + 3HBr
What is the Nitration of Phenol?
When Nitric Acid reacts with Phenol.
The reaction does not require a catalyst.
C6H5OH + HNO3 (Concentrated) → C6H5OH(NO2)3 (2,4,6-Trinitrophenol)
C6H5OH + HNO3 (Weak) → C6H5OH(NO2)3 (2-Nitrophenol)
What are 2- and 4- Directing Groups?
Positions on the Phenol where certain molecules preferance when reacting in 2,4 positions. (also 6 however symetry)
They donate electrons into the ring, increasing the reactivity of Phenol.
eg OH and NH2
What are 3- Directing Groups?
Positions on the Phenol where certain molecules preferance when reacting in 3 position. (also 5 however symetry)
They withdraws electrons from the ring, decreasing the reactivity of Phenol.
eg NO2
