chem whatarethemechanismsofchemicalchange
Reactivity 3.3.3 - radicals take part in substitution reactions with alkanes, producing a mixture of products
see convention for depicting organic reaction mechanisms
halogenation occur via a radical mechanism
- alkanes contain strong
and bonds which take a lot of energy to break - alkanes are non-polar, so do not attract nucleophiles or electrophiles
- so are relatively unreactive compounds
- are regarded as kinetically stable due to high activation energies
however, they are thermodynamically unstable compared to the products
radical substitution reactions occur in 3 stages
- alkanes are saturated, so they mainly undergo substitution
eg
once formed, the radicals will start a chain reaction where a mixture of products including the halogenoalkane is formed
initiation
- formation of radical species
- eg photolytic fission of chlorine
propagation
- the radicals formed in initiation react with other species forming new radicals
- many possible propagation steps allowing the reaction to continue
for example:
termination
- remove radicals from the mixture when they react with each other
- pair up their electrons to form a covalent bond
for example:
the reaction mixture may contain mono- and disubstituted halogenoalkanes, as well as