Protonierung von Amino‐ und Hydroxypyrimidinen NMR‐Spektren und Strukturen der Mono‐ und Dikationen

Proton‐NMR. spectra of amino‐ and hydroxypyrimidines including biologically important bases have been measured in four solvents: CF3COOH, CF3COOHSO2, FSO3H and FSO3HSbF5–SO2 at 27° and −55°C. In CF3COOH mono‐cations are formed, whereas in FSO3H and FSO3HSbF5–SO2 double protonation occurs. In each case the structures of the protonated species are derived from the chemical shifts of CH, NH and OH protons and proton‐proton spin coupling constants. A combination of the measurements described leads to a complete assignment of all proton resonances of the protonated pyrimidines. This approach is also recommended for the structural determination of heterocyclic compounds.