[CBPQT]

Given that the first step in the S_N1 reaction is the slow spontaneous heterolytic cleavage to form a substituted carbocation and a free halide, is it possible for rearrangements to occur when you would just put a suitable haloalkane in solution?

See the attached reaction.
After heterolytic cleavage of the bromide in 2-bromo-3-methylbutane, a hydride shift occurs to form the more stable teriary carbocation. Reattachement of the bromide would give 2-bromo-2-methylbutane.

Would it be possible for this side-reaction to occur spontaneously and would it be significant?

Thanks in advance for any insights!

[pgk]

Both reactions will occur simultaneously.
But according to your opinion, which reaction will occur in preference; the one involving the more stable, tertiary carbocation or the other one that involves the less stable, secondary carbocation?

[CBPQT]

Both reactions will occur simultaneously.
But according to your opinion, which reaction will occur in preference; the one involving the more stable, tertiary carbocation or the other one that involves the less stable, secondary carbocation?

Thanks for showing in interest in my question!

Since the first step is slow, I suppose under thermodynamic conditions, the tertiary carbocation will be the main product. But would you suspect this isomerization is something likely to occur when just dissolving the secondary bromide under standard-ish conditions?

[pgk]

As you have already mentioned, the formation of a carbocation is slow and it is the rate determinative step of the reaction; in contrast the hydrogen shift, which is very fast. Consequently, isomerization will be predominant under both thermodynamic and kinetic conditions, when using acidic catalysts (e.g. organometallic ones that are Lewis acids). But this doesn’t happen under basic conditions (e.g. SN2 nucleophilic substitution of the secondary bromide) that practically no isomerization occurs.