Hi,

Good questions

1) If the final carbocation results in the same degree/same stability, which shift is preferred over the other?

If you have the same stability for two possible products, in all likelyhood you might get a 50/50 mix of the two. It's hard to say for sure, and it's probably not the type of thing the MCAT would make you guess. Normally the examples you get are enzymes, so they'll either indicate the one you would get or it would be difficult to ask a question based on this type of concept.

2) If a shift occurs to the carbocation before the nucleophile attacks in sn1 rxn, will the final product be made of multiple different compounds? Will the major product be the one where the shift occurred?

Theoretically, you could get a mixture of products, but it's more likely that almost all of the product will be from attack on the most stable carbocation - which is the one formed after a hydride shift - consequently any minor products are likely insignificant compared to the major product.

OChem in 2nd year often emphasizes mixtures of products, but because enzymes are magic beasties, mixtures don't really come up on the MCAT in the same prevalence as in regular OChem.

Please let me know if this is unclear.

Katt