Microscale Chemistry Experimentation for Teachers
A basic version of
radical substitution was given in order
to explain the experiment. For secondary schools
a higher level of molecule / radical modelling is developed:
20.
Reaction mechanism
"Radical
Substitution"
(advanced
version)
Photo 1:
The organic substition
type
reaction between hexane and bromine (activated by light) is represented
by one equation and by bead models using big blue
beads for R,
black
beads for
C atoms, white beads
for H atoms and green beads for Br
atoms.
The blue bead represents
an R-group which is C5H11-.
1. Start Reaction
Br2 molecules
are cleaved releasing each two Br radicals.
2. Chain Reaction a
A hexane molecule
reacts with a
bromine radical attracting one hydrogen
atom (with its electron) leaving an hexyl radical and
producing an HBr molecule.
Chain Reaction b
A hexyl radical
reacts with a bromine molecule producing a bromohexane
molecule and releasing a bromine radical.
(This chain reaction goes
on until all the bromine is consumed. Then the remaining hexylradicals
undergo the terminating reaction).
3. Terminating Reaction
Two hexyl radicals
join to produce a 12-C alkane.
Proton exchange reaction
between HBr and water