How do I know which product will occur when different conditions which favors different reactions are all together?
For example: Let's say that I have a secondary substrate (which doesn't favor anything), I use protic solvent (methanol) which favors E1 and SN1, but I use HS- as a nucleophile (should favor E2) and also heat it which also favors E2. Second example: I have a tertiary substrate in a protic solvent which is likely to become SN1 and E1 product. But what happens if I add a strong base like OH- which favors SN2 and also heat it which favors E2?
How do I know what will be the major product?