[joyj2nd]

"I assume there are formulas to determine how substrates and reagents will react with each other?"

There are rules, yes, of cause. But always the question: how much will react? And not: will I get the (reaction) product? But: how many (different) reaction products will I get. This is actually the reason why you need the purification steps after each reaction. Otherwise you would get an "reaction tree", in the end, byproducts reacting with other byproducts and you would get a, basically infinite amount of different end products.