We  can sum up the order of reactivity
of alkyl halides towards SN1 and SN2 reactions as follows:
For the same reasons, allylic and benzylic halides show high reactivity towards the SN1
reaction The carbocation thus formed gets stabilised through resonance (Unit 8, Class XI) as
shown below:
In the following pairs of halogen compounds, which would undergo
SN2 reaction faster Example 6 6
Example 6