Mechanisms, intermediates and catalysts
The mechanism for a reaction is the detailed set of bond–making and bond–breaking steps leading from reactants and products.There is often more than one plausible pathway for a reaction.
could occur in two steps
or
in a single step
Species like CH3+ which are formed in one step of a process and consumed in a subsequent step are known as intermediates.
For example, the overall reaction CH3Br + OH– 
CH3OH + :Br–
step 1: CH3Br +CH3 + :Br – (C–Br bond breaks)
step 2: H3C+ + :OH– CH3–OH (C–O bond forms)
CH3Br + :OH– → CH3OH + :Br–
(the C–Br bond breaks and the C–O bond forms simultaneously)
+CH3 + :Br – (C–Br bond breaks)step 2: H3C+ + :OH–
CH3–OH (C–O bond forms)CH3Br + :OH– → CH3OH + :Br–
(the C–Br bond breaks and the C–O bond forms simultaneously)
could occur in two steps
or
in a single step
Species like CH3+ which are formed in one step of a process and consumed in a subsequent step are known as intermediates.
Intermediates, like catalysts, do not appear in the overall equation for the reaction.
Catalysts are different to intermediates in that they are a reactant in one step and a product in a subsequent step.
Catalysts are different to intermediates in that they are a reactant in one step and a product in a subsequent step.