REACTION MECHANISMS

Alkanes - Radical Substitution
1. Initiation
  1. In the first stage, radicals are formed. Ultraviolet radiation provides the energy to break the covalent bond in a bromine molecule, Br-Br. The bond breaks by homiletic fission. Br2 --> 2Br-
2. Propagation
  1. In the second stage, the products are made. Br- + CH4 --> CH3- + HBr CH3- + Br2 --> CH3Br + Br-
  2. Bromine radicals catalyse the propagation stage. They are not used up in the overall reaction
  3. A bromine radical is used up in the first step and regenerated in the second
3. Termination
  1. Two radicals combine
    1. CH3- + Br- --> CH3Br
    2. Br- + Br- --> Br2
    3. CH3- + CH3- --> C2H6
Alkenes - Electrophilic Addition
1. In this type of reaction the halogen adds across the double bond as shown:
Halogenoalkanes - Nucleophilic substitution
1. In this type of reaction the nucleophile (OH-) attacks the back of the carbon atom, donating an electron pair. A new bond is formed and the carbon-halogen bond breaks
NUCLEOPHILE is an electron pair donor
AN ELECTROPHILE is an electron pair acceptor

Resource summary

	Created by Alessandra Genco over 10 years ago