Why is the top SN2 reaction faster? (Molecular Orbital Theory)

I'm having trouble understanding why the top SN2 reaction proceeds faster. I know that benzylic and allylic halides react faster in SN2 reactions than non-conjugated halides. I think it's because the transition state is more stable but how can you explain that using MO Theory?


[![m](https://i.stack.imgur.com/F6VrP.png)](https://i.stack.imgur.com/F6VrP.png)



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> This is what my professor drew for this question but I don't understand it all. Any help would be appreciated :)
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[![Why is the top SN2 reaction faster?](https://i.stack.imgur.com/A6I2z.png)](https://i.stack.imgur.com/A6I2z.png)


