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Answers to the Exercises "SN/E Competition"


Chemoselective E2 eliminations with primary alkyl halides require very bulky, sterically-demanding bases, otherwise the SN2 reaction would be considerably favoured. DBN is such a very bulky, sterically-demanding and non-nucleophilic base. The ethoxide anion is a strong base. However, it is much less bulky than DBN and, in addition, a good nucleophile. As a result, with sodium ethoxide, an SN2 reaction would considerably exceed the E2 elimination. The thiomethoxide anion is a very good nucleophile and, in addition, a weak base. Therefore, with thiomethoxide, virtually exclusively an SN2 reaction would occur.

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