UPDATED: Apr. 15, 2021 Most of us who’ve worked in chemistry know about logP. The partition coefficient makes it into Lipinski’s rule of five and most post-secondary educations. But when it comes to logP, we mean one exact chemical structure. If a compound ionizes, it’s not the same structure. And since most compounds investigated in pharmaceutical and pharmacological research contain ionizable sites, it’s not logP we should be concerned about, but logD.