Abstract: An unknown white solid compound is very soluble in water.Its single crystal is not obtained now.The NMR technique plays an important role in determining its structure.From the routine ¹H NMR spectrum (Fig.1),¹³C NMR spectrum,decoupling without NOE ¹³C NMR spectrum,off-resonace ¹³C NMR spectrum,(Fig.3),¹H-¹H COSY spectrum (Fig.2),and ¹³C-¹H correlated 2D spectrum (Fig.4),it proves that there are an alkylchain X-CH₂-CH₂-CH₂-Y and an aromatic group Y in this compound.¹³C-¹H correlated spectrum via long range couplings (in inverse probe)(Fig.5) may determine how to connect between the chain and the group.So its main skeletal must be X-CH₂-CH₂-CH₂-Y.IR spectrum (Fig.6),shows us theexistance of the-SO₃-group.From the results of element analysis and MS spectrum,including FAB-MS spectrum (Fig.7 and 8),It was finally judged that the molecular structure of this compound should be the internal salt of pyridinium-N-propane-sulfonic acid.Its structural formula is .

Key words: Structural analysis, Internal salt of pyridinium-N-propane-sulfonic acid, 1D and 2D NMR, FT-IR, FAB-MS