1H, 13C, 15N NMR and Ab Initio/IGLO/GIAO-MP2 Study of Mono-, Di-, Tri-, and Tetraprotonated Guanidine1

Mono- and diprotonated guanidines were prepared in superacid solutions and studied by 1 H, 13 C, and 15 N NMR spectroscopy. The structures, energies, and NMR chemical shifts were also calculated by ab initio/IGLO/GIAO-MP2 method. Excellent agreement were found between experimental and calculated 13 C and 15 N NMR chemical shifts. No persistent triprotonated guanidine was observed. Tri- and tetraprotonated guanidines were also studied by ab initio/IGLO/GIAO-MP2 method.