2
$\begingroup$

For example, given the reaction below:

enter image description here

The substrate is secondary, the solvent is aprotic and it is to react with a strong bulky base. From this, I assumed that the reaction would be $\ce{E2}$. However, it instead begins with an acid-base reaction where the tert-butoxide removes the proton of hydroxide and then proceeds with a $\ce{Sn1}$ reaction where the oxygen attacks the carbon of the leaving group to form an epoxide.

How can you determine if an acid-base reaction will take place before proceeding with a substitution reaction?

$\endgroup$
3
$\begingroup$

Acid-base reactions (like the one shown, involving proton transfer between electonegative atoms) are almost always extremely fast - for all practical purposes instantaneous (diffusion-controlled), and therefore much faster than substitution reactions. In the example given, the bromocyclohexanol is of comparable acidity to tert-butanol (maybe even more acidic), so we would expect instant proton transfer, and the observed result.

The initial proton transfer might not be so favorable if you used a much weaker base, so you could get a different result - or no reaction.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.