Question

hypothesize why a tertiary alcohol is a good solvent for an sn2 reaction where CsF is the nucleophile and iodide is the leaving group there are various electrophiles that iodide is leaving from who's identities don't seem to matter.

from everything I've learned up to now protic solvents are NOT good solvents for sn2 rxns. there have been numerous articles on a research project where 18F is being used for radiolabeling in biological systems and they used tert-amy-alcohol for the solvent in the rxns with the highest yield.

Why did a nonpolar protic solvent work so good for this particular sn2 reaction? if you look up tert-amy-alcohol good solvent for sn2 I'm positive you'll find the article but nowhere can I find answer as to why it's a good solvent for sn2.

thank you

Answer 1

SN2 reaction proceeds in a single step through the formation of a transition state.

i.e. SN2 reaction doesn't involve the formation of any carbocation/carbanion intermediates, for which a polar solvent like ethanol/methanol/isopropanol/water is needed.

That is why a nonpolar solvent like tert-amyl alcohol is needed in order to disfavor the formation of any ionic intermediate.