The underlying problem is therefore how to define a small difference on a molecular level, since each kind of activity, e.g. reaction ability, biotransformation ability, solubility, target activity, and so on, might depend on another difference.
Problem se u znatnoj meri svodi na način na koji se definišu male razlike na molekulskom nivou, pošto svaka vrsta aktivnosti, npr. reakciona sposobnost, biotranformaciona sposobnost, rastvorljivost, aktivnost na biološkom cilju, itd, može da bude zavisna od drugačijih razlika.