A concerted reaction is a reaction in which 1) # covalent bonds broken + #covalent bonds formed > 1, 2) # steps = 1.
eg. 1:
mechanism: The reaction is a nucleophilic aliphatic substitution occurring via SN2 mechanism.
# covalent bonds broken = 1
# covalent bonds formed = 1
# covalent bonds broken + # covalent bonds formed = 1 + 1 = 2
# steps = 1
Thus, the reaction is a concerted reaction.
eg. 2:
mechanism: The reaction is an electrophilic addition.
# covalent bonds broken = 2
# covalent bonds formed = 2
# covalent bonds broken + # covalent bonds formed = 2 + 2 = 4
# steps = 1
Thus, the reaction is a concerted reaction.
see also pericyclic reaction
