[ineedyourhelp]

What functional group can't undergo deuterium exchange in h-nmr?

hydroxyl (oh)
amino (nh, nh2)
thiol (sh2)
methylene (ch2)

thanks a bunch!

[sjb]

What defines whether exchange happens?

[ineedyourhelp]

Nevermind! I figure it out. Thanks though!!

[sjb]

Care to share, after all you came here looking for help - why not help others in the future and post your conclusions.

[ineedyourhelp]

I am pretty sure that the answer is the methylene b/c the first three don't have a characteristic chemical shift  and therefore are reacted with D2O so that the peak of that specific group will disappear. 

[sjb]

Whilst I have no issues with the second part of the answer, I'm not really convinced by the first part. Methylenes can resonate anywhere from ~ 0-7 delta, depending on their exact environment, as indeed can the other protons so I don't think "characteristic chemical shift" can really be defined here. At a simple level, you're right, but I would not be that surprised to see the methylene in e.g. acetylacetone also undergoing exchange (perhaps a bit slower than the amine or similar) - do you appreciate why?