Ethene C2H4
Introduction
Organic compounds which are composed,
of only carbon and hydrogen atoms are known as hydrocarbons. Those hydrocarbons
in which all the valencies of carbon atom are not fulfilled by hydrogen atoms
and double bonds are present between carbon atoms are called Unsaturated
Hydrocarbon or alkenes.
The first member of alkene family
composed of two carbon and four hydrogen atoms and is known as Ethene.
Structure of Ethene
Ethene is an unsaturated hydracarbon,
which is composed of two carbon and four hydrogen atoms. Its molecular formula
is C2H4. The structural formula of ethene shows that each carbon contains two
hydrogen and double bond is present two carbon atoms.
H2C = CH2
Each carbon atom of ethene is Sp2
hyberidized which contains three equivalent partially filled Sp2 hybrid
orbitals and unhyberidized Pz orbital. The hybrid orbitals are arranged at the
three corners of coplaner triangle with an angle of 120º.
Two Sp2 hybrid orbitals of carbon
atoms overlapp with s atomic orbitals of hydrogen atoms to form a sigma bond
between C – H due to the overlapping of Sp2 – S orbitals. The remaining Sp2
hybrid of each carbon atom overlapp with the Sp2 hybrid orbital of other carbon
atom to form sigma bond between C – C due to the overlapping of Sp2 – Sp2.
The unhyberidized Pz orbital of each
carbon atom are situated perpendicular to the Sp2 plane and parallel to the
unhyberidized Pz orbitals of two different carbon atoms overlap side by side to
form a pi bond between carbon atoms.
Diagram Coming Soon
Diagram Coming Soon
Preparation of Ethene
Ethene can be prepared by the
following methods.
1. From Dehydrohalogenation of Ethyl Halide
Removal of hydrogen halide from a
compound is called Dehydrogenation. When mono halo ethane or ethyl halide is
treated with alcoholic potash (KOH), then dehydrohalogenation takes place as a
result ethene is formed.
C2H5X + KOH —-> H2C = CH2 + H2O +
KX
C2H5Cl + KOH —-> H2C = CH2 + H2O +
KCl
2. From Dehalogenation Of Vicinal Dihalide
Removal of halogen from a compound is
called Dehalogenation. Those dihalides in which hydrogen atoms are attached
with two adjacent carbon atoms are called Vicinal Dihalide or 1, 2 – dihalo
ethane reacts with powdered zinc metal then dehalogenation takes place as a
result Ethene is formed.
C2H4X2 + Zn —-> C2H4 + ZnX2
C2H4Cl2 + Zn —-> C2H4 + ZnCl2
3. From Dehydration of Ethyl Alcohol (Ethanol)
Removal of water molecule from a
compound is called Dehydration. In presence of catalyst concentrated H2SO4,
when ethyl alcohol or ethanol is heated at about 170ºC then Dehydration takes
place as a result ethene is formed.
C2H5OH —-> C2H4 + H2O
Dehydration of ethanol can also be
called out in following two ways.
1. In presence of catalyst Al2O3 when
ethanol is heated at (350 – 360ºC), then ethene is formed
C2H5OH —-> C2H4 + H2O
2. In presence of mixture of Al2O3
and H3PO4 at 250ºC, when ethanol is heated then ethene is formed.
C2H5OH —-> C2H4 + H2O
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