1. Nucleophilic Substitution
Halogenoalkanes

2. Starter Try and write definitions for these key words. Halogenoalkane
Nucleophile
Electrophile
Electronegativity

3. What do Nucleophiles do?
These species are electron pair donors
They will donate a pair of electrons to something that doesn’t have enough electrons (areas of low electron density)
Common examples include, cyanide ions, ammonia and hydroxide ions and even water.

4. Nucleophilic substitution
Nucleophilic substitution definition: An electron rich species (nucleophile) attacks an electron deficient atom to remove another atom or group of atoms in a molecule.
e.g. CH3Cl OH-  CH3OH + Cl-

5. Nucleophilic substitution
hydroxide ion with bromoethane
mechanism
CH3CH2Br
+ OH-
(aqueous)
CH3CH2OH + Br-
ethanol
cyanide ion with iodoethane
mechanism
CH3CH2I (ethanol)
+ CN-(aq)
CH3CH2CN + I-
propanenitrile
ammonia with bromoethane
mechanism
CH3CH2Br
+ NH3 2
CH3CH2NH2
+ NH4+Br-
aminoethane

6. hydroxide ion with bromoethane
Nucleophilic substitution mechanism
hydroxide ion with bromoethane
CH3 H Br C
CH3 H OH C + - Br - - OH
ethanol
reaction equation

7. cyanide ion with iodoethane
Nucleophilic substitution mechanism
cyanide ion with iodoethane
CH3 H I C
CH3 H CN C + - I - CN -
propanenitrile
reaction equation

8. ammonia with bromoethane
Nucleophilic substitution mechanism
ammonia with bromoethane
CH3 H Br C H
CH3
NH2 C + Br - + -
NH3
NH3
CH3 H
NH2 C
H NH3+Br -
aminoethane
reaction equation

9. Knowledge Check Draw mechanisms for the following reactions:
Chloromethane + Sodium Hydroxide  Methanol + Sodium chloride
1-iodo-2-chloroethane + Hydrogen cyanide  1-cyano-2-chloroethane + Hydrogen iodide
1-chloro-2-bromo-3-iodopropane + ammonia  1-amino-2-bromo-3-iodopropane + ammonium chloride

10. Preparation of Alcohols
Nucleophilic substitution reactions are used to prepare alcohols from halogenoalkanes. E.g butan-1-ol from 1-bromobutane.
The OH- nucleophile is provided by aqueous sodium hydroxide.
The reaction is very slow. To increase the rate of the reaction, the reactants are heated.
The reaction is done under reflux to prevent loss of liquids through evaporation.

11. Reflux Apparatus
Upon heating, the liquids evaporate and escape form the flask, however the condenser cools these vapours, turning them back into a liquid which drips back into the reaction vessel.
The reaction can continue for as long as necessary with no loss of material.

12. Nucleophilic substitution
When hydroxide ions (e.g. NaOH) or water is used the reaction is again nucleophilic substitution but can also be called hydrolysis.
Hydrolysis involves a chemical reaction where water or hydroxide causes the breaking of a bond in a molecule.

13. Knowledge Check