Knowledge Bank

Replacement of hydrogen atoms in melamine [2,4,6-triamino-$\ast \ast$-triazine or $C3N3(NH2)3$] by one, two, or three guanyl groups $[-C(:NH)NH2]$ yields a series of molecules with a framework of alternate carbon and nitrogen atoms. They are all relatively strong bases, adding one proton per guanyl group. Two strong absorption bands are found in the 2000 to 3000 {\AA} region. The longer wavelength band is the stronger for the free bases, while the reverse is true for the corresponding acids. (These acid spectra resemble previously reported substituted triazine spectra.) In the case of monoguanyl melamine the two most probable structures of the free base are tautomers. Addition of a proton is assumed to remove this difference. Correlation of the observed spectral change with postulated changes permits a choice between the proposed free base structures. Similar considerations apply to the other guanyl melamines.