N mechanism , analogous to the S N 2 mechanism, requires good leaving groups.
TsO - > I - > Br - > H 2 O > Cl -
Water does not react with 2-Fluoropropane since fluorine is a bad leaving group, but it does with 2-Bromopropane.
[1] Reaction does not take place (Fluorine bad leaving group)
The leaving group influences the rate of S N 1, since the slow step in the mechanism is dissociation from the substrate. The better the leaving group, the faster the reaction.
[3] Quick reaction
[4] Slow reaction (chlorine worse leaving group than fluorine)
tert-Butyl bromide ionizes faster than tert-butyl chloride, because bromine is a better leaving group than chlorine. As the dissociation of the substrate is the slow step of the mechanism, the first reaction is faster than the second.
