ISSUE:

In most of the examples that I am studying, "ideal" cases usually appear, this leads me to wonder what would happen in a case like this: What

type of reaction would a secondary substrate give, for example, isopropyl bromide, if we "combined badly" solvent and nucleophile.

For example case1:
Protic solvent H2O + good nucleophile CN-

case2:
Aprotic solvent DMSO + CH3-OH

Let's say that my question is about which way the mechanism would "lean" in these cases.

If the solvent or the nucleophile has more influence on the mechanism. I intuit to think, I don't know if correctly or perhaps I should consider more variables, that in these cases I would still have to compare the leaving group with the nucleophyllic.

For example: In case 1, between CN- and Br- I think that CN- is a better nucleophile, HBr is a much stronger acid and therefore Br- is not very basic.
CN- will be a bit more basic and better nucleophile, although I'm not considering polarizability or anything like that. This leads me to think that CN- can attack before Br- dissociates and that is why it would go through a Sn2 mechanism.

In case 2 the opposite occurs, Br- is a better nucleophile than CH3-OH, that is why I think that Br - It would have a faster exit and then it would attack the methanol through Sn1.

In the end, in these cases I give priority to the nucleophiles over the solvent.

But I don't know if this is correct. Or I should consider things in another way. PS: Sorry for the accents, I'm writing this a little late and my typing isn't the best, also sorry if I've asked too many questions in the last few days, the exams are coming up and I'm trying to go over every little detail.

Greetings and thanks for maintaining a forum of this quality

Hello, sorry for the delay in answering you.
In case 1, having a good nucleophile and being a secondary substrate, SN2 will be in the majority.
However, the solvent slows down the cyanide attack and some molecules could evolve through carbocation formation. In both cases the product would be the same. If we are interested in a maximum performance of SN2 we should use an aprotic solvent.

In case 2, methanol is poorly nucleophile and is not capable of giving SN2, therefore the mechanism followed is SN1, which can be accompanied by small amounts of E1.

In that case, if the methanol was dissolved in water or just pure methanol, we would have a faster reaction. Now that I have continued reading your post, I see that you have answered yourself correctly.

I send you a greeting!!!

Thank you very much german for the answer, the wait is worth it. It would not occur to me to demand immediacy in such disinterested help. I send you a greeting!