The Haloalkanes
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- Created by: francesca_321
- Created on: 10-03-15 19:23
What happens with alkanes in the presence of UV lights?
react with chlorine to form a micture of products with the halogens substituting hydrogen atoms
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What is the overall equation of the synthesis of chloroalkanes?
CH4 + CL2 ---> CH3CL +HCL
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What is the mechanism for this reaction called?
Free radical substitution
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what are the three steps involved?
Initiation, propagation and Termination
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What is a condition for initiation?
UV light
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What does the UV light do?
it supplies energy to break the CL-CL bond. It is broken in preference to others as it is the weakest
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What is the process called where the bond has broken?
homolytic fission
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What does this reaction form?
Free radicals
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What do free radicals not have?
a charge
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What is the definition of a free radical?
a reactive species which possess an unpaired electron
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What is the first stage of propagation?
CH4 + CL- --> HCL + .CH3
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What are chlorine free radicals?
very reactive and remove an H from the methane leaving methyl
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What happens with the methyl free radicals?
It reacts with a cl2 molecule to produce the main product and another cl free radical
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what do all propagation steps have in the reactants and the products?
free radical
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What is the second stage of propagation?
.CH3 +CL2 ---> CH3CL +CL-
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As the free radical is regenerated what can it do? in what?
It can react with several more alkane molecules in a chain reaction
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Why is step termination called termination?
Collisions of two free radicals does not generate further free radicals: so thechains is terminated
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What is one reaction in termination?
.CH3 + CL- -----> CH3Cl
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What is the second equation?
.CH3 + .CH3 ------> CH3CH3
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What is CH3CCL3 used as?
the solvent in dry cleaning
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What does the naturally occuring ozone layer in the upper atmosphere do?
It filiters out much of the sun's harmful UV radiation
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What is the definition of a nucelophile?
Electron pair donator eg: OH-, NH3 and CN-
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What do the curly arrows show?
it shows the movement of two electrons
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What does the rate of substitution depend on?
the strength of the C-X bond
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What does this mean?
The weaker the bond, the easier it is t break and the faster the reaction
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What is hydrolysis defined as?
The splitting of a molecule by a reaction with water
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what is water and what can it do?
It is a poor nucleophile but it can react slowly with halo-alkanes in a substitution reaction
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What does a precipitation formation mean?
The quicker the precipitate is formed, the faster the substitution rection and the more reactive the haloalkane
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What does this substitution reaction depend on?
The strength of the C-X bond
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What is formed in a nucleophilic reaction with aqueous hydroxide ions?
Change in functional group haloalkane ----> alchohol
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What is the reagant in this reaction?
potassium or sodium hydroxide
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What conditions are needed?
In aqueous solution
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What is the mechanism?
Nucleophilic substitution
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What is the type of reagent?
Nucleophile, OH-
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Why are aqueous conditions needed?
If the solvent is changed to ethanol an elimination reaction ccours
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What is happening in nucleophilic substitution with CN ions?
Change in functional group: haloalkane to nitrile
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What is the reagent in the reaction?
KCN dissolved in ethanol
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What are the conditions?
heating under reflux
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What is the mechanism?
nucleophilic substitution
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What is the type of reagent?
Nucleophile, CN-
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What is the change in functional group in nucleophilic substitution with ammonia?
Haloalkane to amine
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What is the reagent?
NH3 dissolved in ehtanol
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What are the conditions?
heating under pressure
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What happens between the haloalkane and the amines formed?
further substitution reactions
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What does this lead to?
A lower yield of the amine
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How can this be minimised?
Using excess ammonia
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What do the chlorine free radicals do in the ozone layer?
they catalse the decomposition because they are regenerated
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What is the fist equation in the ozone layer?
Cl. +O3 -----> ClO. +O2
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What is the second equation?
CLO. + O3 -----> 2O2 +CL.
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Other cards in this set
Card 2
Front
What is the overall equation of the synthesis of chloroalkanes?
Back
CH4 + CL2 ---> CH3CL +HCL
Card 3
Front
What is the mechanism for this reaction called?
Back
Card 4
Front
what are the three steps involved?
Back
Card 5
Front
What is a condition for initiation?
Back
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