I don’t know how many readers out there use the cLogP function in ChemDraw, but you might want to take a look at the illustration here before you use it again. A reader alerted me to this glitch: drawing in explicit hydrogens sends it into an even stranger world of fantasy than most calculated logP values inhabit. There seems to be a limit, though, as that cyclopropane series illustrates. (Note that the “logP” function resists temptation).
PerkinElmer says that there are several logP calculating functions built in, but that cLogP is from BioByte. I don’t think that they got their money’s worth from them. Now, this isn’t the first glitch like this I’ve seen – a lot of chemical drawing and searching programs choke on details here and there. But this is the sort of thing you’d have thought would have been fixed by now.
Update: it has indeed been fixed, according to the fast-acting Phillip Skinner at PerkinElmer. But apparently many of us out in user-land aren’t using updated versions. For what it’s worth, I have ChemBioDraw Ultra 13.02 v. 3020 – are others getting more reliable numbers with newer software?
Note: here’s where the patch can be downloaded.