Characterization of biguanides by 15N NMR spectroscopy

The monoprotonated biguanides phenformin hydrochloride, buformin hydrochloride and metformin hydrochloride were investigated by 15N NMR spectroscopy. The structure of all hydrochlorides is best described by a 1,3-diazabutadienic skeleton with three amino groups and its corresponding mesomeric forms. There is no evidence for the presence of other tautomeric forms in solution. Copyright © 1999 John Wiley & Sons, Ltd.