Mechanisms
Substitution – Where one group is replaced/ substituted by another.
Elimination – Where two groups are replaced by another.
Addition (reverse of elimination) – Where two groups are added across a
double bond.
Rearrangement – Where scrambling of structure occurs, things move
around but are not replaced.
Mechanisms are often explained using
curly arrows
Reversible reaction, but equilibrium lies to
the right
Arrow pushing is the movement of
electrons.
Electrons typically flow from areas of high
electron density to areas of low electron
density.
What is a mechanism
Tells you how bonds break, when bonds form, and why the reaction takes
the path it does.
It shows electron movement, bond breaking and forming, intermediates
(like carbocations, radicals or transition states) and rate determining
steps.
o What happens during the hydrolysis of tertbutyl bromide (SN1)?
(CH3)3CBr+H2O→(CH3)3COH+HBr
The mechanism explains:
C-Br bond breaks first when it reacts with water – carbocation forms
Water (nucleophile) attacks the carbocation, and the carbon is now
bonded to OH.
Substitution – Where one group is replaced/ substituted by another.
Elimination – Where two groups are replaced by another.
Addition (reverse of elimination) – Where two groups are added across a
double bond.
Rearrangement – Where scrambling of structure occurs, things move
around but are not replaced.
Mechanisms are often explained using
curly arrows
Reversible reaction, but equilibrium lies to
the right
Arrow pushing is the movement of
electrons.
Electrons typically flow from areas of high
electron density to areas of low electron
density.
What is a mechanism
Tells you how bonds break, when bonds form, and why the reaction takes
the path it does.
It shows electron movement, bond breaking and forming, intermediates
(like carbocations, radicals or transition states) and rate determining
steps.
o What happens during the hydrolysis of tertbutyl bromide (SN1)?
(CH3)3CBr+H2O→(CH3)3COH+HBr
The mechanism explains:
C-Br bond breaks first when it reacts with water – carbocation forms
Water (nucleophile) attacks the carbocation, and the carbon is now
bonded to OH.
