The potential energy profiles of the following S(N)2 reactions were obtaine
d using the G2 quantum chemical method: H3N + CH3OH2+-->+H3NCH3 + H2O, H2O
+ CH3FH+-->+H2OCH3 + FH and H3N + CH3FH+-->+H3NCH3 + FH. The activation ene
rgy for the first is only Delta E degrees = 6.9 kJ mol(-1), while the other
s have no energy barrier. These findings are discussed in the light of Marc
us theory.