Unit 14: Applications of Organic Chemistry Learning Aim B: Understand the reactions
and properties of aromatic compounds.
Index.
Introduction,
Structure of Benzene (sigma and pi bonding),
Chemical properties of industrially important benzene and monosubstitutents
benzene compounds,
Mechanism’s for addition and substitution reactions of benzene,
Effects of different monosubstituents on the benzene ring,
Introduction.
This report will explain the structure of benzene using sigma and pi bonding, providing evidence for
the structure, explain the chemical properties of industrially important benzene and monosubstitutents
benzene compounds. Compare the mechanisms for addition and substitution reactions of benzene
and finally analyse the effects of different mono substituents on the benzene ring to predict further
substitution positions of a reaction species on the benzene ring.
Structure of Benzene.
Benzene only contains Hydrogen and Carbon atoms so it is classed as a hydrocarbon. Benzene
reacts with chlorine or bromine in the presence of a catalyst (that is either aluminium chloride or
aluminium bromide). It also has a hexagon structure because the planar structure is the only way that
the 6 p orbitals can overlap above and below the ring of carbon and give the delocalised pi system.
1
, Halogenation C6H6 C6H5Cl + HCl (Chlorobenzene)
Nitration C6H6 C6H5NO2 + H2O (Nitrobenzene). Nitration is where one of the hydrogen atoms is
replaced by a nitro group. (Conditions; H2SO4 conc HNO3 temperature below 50°C)
Benzene is a cyclic structure that has a hydrogen bonded to each of it’s 6 carbons, it has 6 sigma
bonds between carbon atoms with 3 pi bonds that alternate and each carbon atom has 4 electrons in
bonding electron pairs, 3 of which are in sigma bonds whereas one contributes to a pi bond.
Sigma bonds are formed by the overlapping of atomic orbitals head-to-head, while pi bonds are
formed by the lateral overlap of two atomic orbitals. Both sigma and pi bonds are types of covalent
bonds and pi bonds are usually weaker than sigma bonds as pi bonds are generally more spread out
than sigma bonds.
A single bond is a sigma bond and a double bond contains one sigma bond and one pi bond.
Benzene has 12 sigma bonds and 3 pi bonds as it consists of 9 single bonds and 3 double1 bonds
therefore benzene has 12 sigma bonds and 3 pi bonds
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map
%3A_Organic_Chemistry_(McMurry)/15%3A_Benzene_and_Aromaticity/
15.03%3A_Structure_and_Stability_of_Benzene (03/04/21)
Graphs such as the one above reveal the distance at which the energy is at its minimum. The
stronger the bond between atoms the higher the bond energy is and the smaller the distance between
the two atoms.
Key Terms.
Equilibrium bond length: Typical distance between two atoms when they are bonded to
each other,
Morse curve: Plot showing the dependence of the energy related with a system of two
atoms on the distance between them,
Enthalpy: In thermodynamics, a quantity of the heat content of a chemical or physical
system, measured under conditions of continuous pressure,
2
and properties of aromatic compounds.
Index.
Introduction,
Structure of Benzene (sigma and pi bonding),
Chemical properties of industrially important benzene and monosubstitutents
benzene compounds,
Mechanism’s for addition and substitution reactions of benzene,
Effects of different monosubstituents on the benzene ring,
Introduction.
This report will explain the structure of benzene using sigma and pi bonding, providing evidence for
the structure, explain the chemical properties of industrially important benzene and monosubstitutents
benzene compounds. Compare the mechanisms for addition and substitution reactions of benzene
and finally analyse the effects of different mono substituents on the benzene ring to predict further
substitution positions of a reaction species on the benzene ring.
Structure of Benzene.
Benzene only contains Hydrogen and Carbon atoms so it is classed as a hydrocarbon. Benzene
reacts with chlorine or bromine in the presence of a catalyst (that is either aluminium chloride or
aluminium bromide). It also has a hexagon structure because the planar structure is the only way that
the 6 p orbitals can overlap above and below the ring of carbon and give the delocalised pi system.
1
, Halogenation C6H6 C6H5Cl + HCl (Chlorobenzene)
Nitration C6H6 C6H5NO2 + H2O (Nitrobenzene). Nitration is where one of the hydrogen atoms is
replaced by a nitro group. (Conditions; H2SO4 conc HNO3 temperature below 50°C)
Benzene is a cyclic structure that has a hydrogen bonded to each of it’s 6 carbons, it has 6 sigma
bonds between carbon atoms with 3 pi bonds that alternate and each carbon atom has 4 electrons in
bonding electron pairs, 3 of which are in sigma bonds whereas one contributes to a pi bond.
Sigma bonds are formed by the overlapping of atomic orbitals head-to-head, while pi bonds are
formed by the lateral overlap of two atomic orbitals. Both sigma and pi bonds are types of covalent
bonds and pi bonds are usually weaker than sigma bonds as pi bonds are generally more spread out
than sigma bonds.
A single bond is a sigma bond and a double bond contains one sigma bond and one pi bond.
Benzene has 12 sigma bonds and 3 pi bonds as it consists of 9 single bonds and 3 double1 bonds
therefore benzene has 12 sigma bonds and 3 pi bonds
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map
%3A_Organic_Chemistry_(McMurry)/15%3A_Benzene_and_Aromaticity/
15.03%3A_Structure_and_Stability_of_Benzene (03/04/21)
Graphs such as the one above reveal the distance at which the energy is at its minimum. The
stronger the bond between atoms the higher the bond energy is and the smaller the distance between
the two atoms.
Key Terms.
Equilibrium bond length: Typical distance between two atoms when they are bonded to
each other,
Morse curve: Plot showing the dependence of the energy related with a system of two
atoms on the distance between them,
Enthalpy: In thermodynamics, a quantity of the heat content of a chemical or physical
system, measured under conditions of continuous pressure,
2
