Solvents in SN1 and SN2 Reactions

by James

 

{ 2 comments… read them below or add one }

Anthony April 8, 2015 at 9:58 am

I’m still a bit unclear on why the lack of H bonding in polar aprotic will make SN2 faster. The reason for slowing it down was that all those protic molecules arrange themselves around the nucleophile and block it, but wouldn’t the exact same thing happen with the aprotic (there’s still dipole). Is it just that it happens more with polar protic?

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James April 11, 2015 at 2:18 pm

Hydrogen bonding is a stronger force than dipole-dipole interactions. For example compare the boiling point of 2-propanol (82 degrees C) with 2-propanone (56 deg C) which have almost identical molecular weights.

H bonding to the negatively charged nucleophile will be stronger than dipole interactions with that same nucleophile.

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