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Which among these two (1-chloro-1-phenyl-ethane and 2-(chloromethyl)-1,3-dimethylbenzene) is more reactive towards SN2?

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I strongly believe that it should be Y because of lesser hindrance on the electrophilic carbon.

However, the answer key of my exercise book states that X > Y. What's the reason behind that?

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  • $\begingroup$ Which book is this? Could you please mention the source? Thanks! $\endgroup$ – arya_stark Aug 13 '18 at 13:57
  • $\begingroup$ @schrodinger_16 it's himanshu pandey's advanced problems in organic chemistry for JEE $\endgroup$ – Abcd Aug 13 '18 at 18:45
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The correct answer is X because the 2 methyl groups on the Y are bulky enough to cause steric hindrance. Surprisingly, from what I have seen, if you only had one methyl group on Y, the SN2 reaction would proceed.

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    $\begingroup$ Got a reference for that? $\endgroup$ – Waylander Jul 13 '18 at 19:39
  • $\begingroup$ There's plenty of examples of SN2 on dimethyl substrates like Y. Rates are certainly going to be slower, but it's not too difficult of a substrate compared to others. $\endgroup$ – Dennis Cao Jul 13 '18 at 19:45
  • $\begingroup$ Needs a citation. In the reactive conformation, Cl–C–Nu should be parallel to the ring. In the absence of some data I'm skeptical as to how much steric hindrance those methyl groups actually produce. I would be happy to be convinced otherwise, of course. $\endgroup$ – orthocresol Sep 12 '18 at 9:53

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