Arrange compound in image in decreasing order of sn2

I tried it by comparing electron deficiency and steric crowding.so most electron deficiency is at 3 chloro propene due to -I effect of alkene.hence most reactive toward sn2.Now ,how to compare other two?

answer is:3-chloropropene> chloroprapane > chloroethene. how to compare last two?

For comparing first your reason in wrong ..
This is due to extended conjugation
You can get more insights here
Also in third one Cl is in conjugation with double bond which makes it poor leaving group .

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It's obvious because inlast compound u can see the lone pair of Cl takespart in resonance with double bond which make it more stable compared to seond one so SN2 is favourable for second one

You can see the reactivity towards Sn2 mechanism by using the stability of carbocation formed.
Higher the stability of carbocation,lesser will be the reactivity towards Sn2 mechanism.
So the second one has primary carbocation which is highly unstable so more reactive towards Sn2 mechanism.

In option 3 there is resonance between Cl and pie bond so it is not easy to break the bond.

@arush_2019 ,can you try this ionic equilibrium given in link below: