6
$\begingroup$

I came across a question regarding relative rate of solvolysis. According to the answer key:

enter image description here

My analysis:

As in all the three cases, the Cl atom is bounded to a tertiary carbon, hence, all of them are ${S_N1}$ reactions. So, the rate of solvolysis will depend on the stability of the carbocation formed. Upon considering hyperconjugation, t-Bu cation is coming out to be more stable than the tertiary cycloalkyl carbocations.

But, according to the given answer, t-BuCl has the least solvolysis rate as compared to the others. Could anyone please explain why is it so?

$\endgroup$
2
  • $\begingroup$ @NisargBhavsar Even I thought the same initially, and so to confirm, I checked if solvolysis/hydrolysis can involve elimination - In Wikipedia, for hydrolysis, it is mentioned that "The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile". So I think even if we consider E1 instead of ${S_N1}$, we still need to check the carbocation stability to compare. Am I going wrong somewhere? $\endgroup$ – Pal Jun 14 at 16:34
  • $\begingroup$ You are right. Check the answer I posted. $\endgroup$ – Nisarg Bhavsar Jun 16 at 8:05
1
$\begingroup$

According to the definition given by The IUPAC Compendium of Chemical Terminology: The Gold Book[1], solvolysis is defined as:

Generally, reaction with a solvent, or with a lyonium ion or lyate ion involving the rupture of one or more bonds in the reacting solute. More specifically the term is used for substitution elimination and fragmentation reactions in which a solvent species is the nucleophile.

It clearly states that elimination occurring due to a solvent is also considered solvolysis and thus elimination in case of t-butyl is also considered.

This means you are right in your reasoning of t-butyl being the most susceptible to solvolysis among the given choices.

I believe this was an error from the question setter. They must have been referring to the substitution reaction due to the solvent but ended up creating a poorly worded question.


Reference:

(1) The IUPAC Compendium of Chemical Terminology: The Gold Book; Gold, V., Ed.; International Union of Pure and Applied Chemistry (IUPAC): Research Triangle Park, NC, 2019.

$\endgroup$

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.