Substitution reactions of alkanes L.O.: Describe the substitution of alkanes in the presence of ultraviolet radiation. Describe how homolytic fission leads to the mechanism of radical substitution in alkanes. Explain the limitations of radical substitution in synthesis
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Substitution reactions of alkanes L.O.: Describe the substitution of alkanes in the presence of ultraviolet radiation. Describe how homolytic fission.
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Substitution reactions of alkanes
L.O.:
Describe the substitution of alkanes in the presence of ultraviolet radiation.
Describe how homolytic fission leads to the mechanism of radical substitution in alkanes.
Explain the limitations of radical substitution in synthesis
Free radical substitution: Cl2 + CH4
Other products of chain reactionsIf an alkane is more than two carbons in length then any of the hydrogen atoms may be substituted, leading to a mixture of different isomers. For example:
The mixture of products is difficult to separate, and this is one reason why chain reactions are not a good method of preparing halogenoalkanes.
1-chloropropane 2-chloropropane
Further substitution in chain reactionsSome chloromethane molecules formed during free radical substitution between methane and chlorine will undergo further substitution to form dichloromethane. Further substitution can occur until all hydrogens are substituted.
The further substituted chloroalkanes are impurities that must be removed. The amount of these molecules can be decreased by reducing the proportion of chlorine in the reaction mixture.
Task:
Bromine can react with ethane in UV light to give 1-bromoethane
1)Write the corresponding initiation, propagation and termination reactions.
Extension: a) write any other possible products from this reaction. b) Write the corresponding mechanisms.
AlkenesL.O.:
Understand that alkenes and cycloalkenes are unsaturated hydrocarbons.
Explain the overlap of adjacent p-orbitals to form a π-bond.
Explain the trigonal planar shape around each carbon making up the C=C bond of alkenes.
Ethene
Two kinds of bonding orbitals
Sigma bond = The one that makes up all the single bonds we need to know about
Pi bond = A double bond is made from two kinds of bond, one is a sigma bond, the other is a pi bond
Formation of the C=C double bond
A cross section of a pi bond
Shape of an ethene molecule
Cyclohexene
Describe addition reactions of alkenes with both hydrogen and halogens.
Describe the use of bromine as a test for unsaturation.