Friday, December 10, 2010

How many hydrogen-bond acceptor groups does triazole have?

Andrew asked me about the H-bond donor capabilities of 1,2,4-triazole:

Apparently, the way he uses the CDK library, it returns zero H-bond donor groups, as is visible in his application down the bottom of the page. When start from the PubChem entry, it correctly detects on H-bond donor group, so it seems to have to do with implicit hydrogens (not uncommon). Debugging will continue later, when I am done analyzing the Beilstein Journal of Organic Chemistry literature with Oscar.

But, I do like to put this question out in the open: how many H-bond acceptor groups does this triazole have? The CDK calculates 3 groups, while PubChem counts 2. ChemSpider thinks 3 too.

Intuitively, I would agree with the CDK and ChemSpider: the nitrogen which acts as the single H-bond donor still have a free electron pair. What do you think? Is PubChem wrong, or is the CDK and ChemSpider wrong? Can this special nitrogen be both a donor and acceptor at the same time? I think so. However, I do not know how I can easily search CrystalEye for this. Bonus points for answering the Blue Obelisk eXchange question.