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.

outgoing group 01

[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.

outgoing group 02

[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.