Halogenoalkanes
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What are the prefixes for haloalkanes?
Bromo- Iodo- Chloro-
What bond do halogenoalkanes have?
C-X polar bond where X is slightly negative and C is slightly positive. Halogens are more electronegative than carbon.
Why do the C-X bonds get less polar as you go down group 7?
Electronegativity decreases down group 7.
Describe the solubility of halogenoalkanes?
The C-X bonds are not polar enough to make the halogenoalkanes soluble in water.
What are the main intermolecular forces between halogenoalkanes?
Dipole-dipole attractions Van der waal forces.
Describe the boiling points of halogenoalkanes.
Boiling points increase with increased chain lengths. Boiling points increase going down the halogen group. This is due to greater van der waal forces.
What is a nucleophile?
An electron pair donor with a lone pair of electrons.
What is nucleophilic substitution?
A reaction where a nucleophile donates a lone pair of electrons to a slightly positive carbon atom, the slightly negative atom leaves the molecule.
Why is carbon attacked by nucleophiles in nucleophilic substitution?
The carbon is electron deficient as it is slightly positive.
Why is the C-I bond less reactive than the C-F bond?
The C-I bond is less polar than C-F
How does a nucleophile form a covalent bond with the alkane?
By using the lone pair.
What are the 3 common nucleophiles?
:OH- (hydroxide ion) :NH3 (ammonia) :CN- (cyanide ion)
What mechanism do haloalkanes undergo?
Nucleophilic substitution
What does a curly arrow indicate?
Movement of an electron pair.
Where does the curly arrow go in a nucleophilic substitution mechanism?
The lone pair of electrons of the nucleophile is attracted to a slightly positive carbon atom.
Describe the nucleophilic substitution with a hydroxide ion.
Nucleophile - :OH- Reagent - potassium or sodium hydroxide Conditions - In warm, aqueous solution. Change in functional group - halogenoalkane to alcohol. Mechanism - nucleophilic substitution
Describe the nucleophilic substitution with a cyanide ion.
Change in functional group - halogenoalkane to nitrile. Reagent - aqueous KCN dissolved in ethanol Conditions - heating under reflux. Mechanism - nucleophilic substitution Nucleophile - :CN-
Describe the nucleophilic substitution with a ammonia.
Change in functional group - halogenoalkane to amine. Reagent - NH3 dissolved in ethanol Conditions - heating under pressure. Mechanism - nucleophilic substitution Nucleophile - :NH3
How do you test for an alkene?
Use bromine water. Positive result = decolourised (Shows there is a C=C bond)
Are CFC reactive or unreactive?
Unreactive under normal conditions.
Describe elimination with a hydroxide ion.
Change in functional group - halogenoalkane to alkene Reagents - potassium/sodium hydroxide Conditions - in ethanol, heat under reflux. Mechanism - elimination Nucleophile - :OH-
What kind of halogenoalkanes can undergo elimination?
Tertiary and secondary haloalkanes
What kind of halogenoalkanes undergo nucleophilic substitution?
Primary and secondary haloalkanes
What does ozone in the atmosphere do?
It forms naturally in the upper atmosphere as it absorbs UV radiation.