6.3 - Halogenoalkanes And Alcohols
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Which elements are we looking at?
Halogens , Group 7 elements… F, Cl, Br, I, At
What are dihalogenoalkanes?
compounds where atleast one hydrogen in the alkane chain has been replaced by a halgen
Primary, secondary and tertiary?
You work out the stability of the compound; primary is week as it only has one methyl group, tertiary is strong as it has 3 methyl groups.
Fact about the carbon-halogen bond?
it’s polar as the halogen is always more electronegative
What is a nucleophile?
Electron donating, electron rich
What is an electrophile?
Electron pair acceptor, electron defficient
What does the nucleophile do?
Replaces the halogen atom in the halogenoalkane, forming a compound with a different functional group
What happens during the hydrolysis of halogenoalkanes?
The halogen atom is replaced by the hydroxide ion
What is nucleophillic attack?
Hydroxide ion attacks the electron defficient carbon with its lone pair of electrons
How does the carbon- halogen bond break?
Heterolytic fission?
Substitution reactions, with water?
Halide is replaced with OH group, producing an alcohol, this is a hydrolysis reaction.
Substitution reactions, with aqueous potassium hydroxide?
Another way to produce alcohols - very quick Halide is replaced with OH group
Substitution reactions, with potassium cyanide?
Halide is replaced with CN group, which increases the carbon chain length and forms a nitrile This is carried out under reflux with potassium cyanide in ethanol
Substitution reactions, with ammonia?
Halide is replaced with NH2 group, producing an amine Ethanol is used Ammonium salt is also produced
Elimination reactions, with ethanolic potassium hydroxide?
Produces an alkene Heated under reflux hydroxide ion acts as a base
Carbo-cations?
the stability of the carbocation formed, effects the products of a reaction! primary (1 methyl group- very weak) quaternary ( 4 methyl groups- very strong)
Are halogenalkanes soluble in water?
No, as C-H bonds are non polar they need to dissolve in ethanol which is also non polar
do halogenalkanes have a polar bond? why?
Yes, as the halogen has a higher electronegativity than carbon
When do their boiling points increase?
Further down group 7 When the carbon chain length increases
which halogen bond is most polar?
C-F bond, as fluorine is most electronegative
which halogen has the lowest bond enthalpy?
Iodine, therefore the C-I bond is the most reactive
Examples of nucleophiles?
OH-, CN-
What is nucleophilic substitution?
a reaction where a nucleophile donates a lone pair of electrons
what is formed in the elimination reactions of halogenalkanes?
an alkene, water and halogen ion