Zusammenfassung der Ressource
REACTION MECHANISMS
- Alkanes - Radical Substitution
- Initiation
- 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-
- Propagation
- In the second stage, the
products are made. Br- +
CH4 --> CH3- + HBr
CH3- + Br2 --> CH3Br +
Br-
- Bromine radicals catalyse
the propagation stage.
They are not used up in the
overall reaction
- A bromine radical is
used up in the first step
and regenerated in the
second
- Termination
- Two radicals combine
- CH3- + Br- --> CH3Br
- Br- + Br- --> Br2
- CH3- + CH3- --> C2H6
- Alkenes - Electrophilic Addition
- In this type of reaction the halogen adds across the double bond as shown:
- Halogenoalkanes - Nucleophilic substitution
- 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