Friday, 3 June 2016

organic chemistry - How can aqueous KOH give alcohol by SN2 of alkyl halide?


I ask this because SN2 requires a strong nucleophile, and I have read OHX isn't a strong nucleophile in a polar protic solvent like water. So, how can OHX replace, say IX from CHX3I (methyl iodide)?



Answer



When you are considering a particular SN2 reaction, you have to consider the nucleophilicity as well as the nature of the leaving group of both the groups.


Here as you mentioned, OHX and IX (and other halide ions, except FX, which is a very bad nucleophile) have comparable nucleophilicity in protic solvents. But, as for their leaving nature, IX (as well as other halides) is far more better leaving group than OHX, because we know weak bases are better leaving groups. That is why the reaction is feasible.



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