2-Aminothiazolines can exist in two tautomeric species, amino and imino forms, which can theoretically exist as two stereoisomers. Several methods and techniques have been used to evaluate tautomeric process, but in this case 15 N NMR spectroscopy was used due to tautomeric process involves two nitrogen atoms. In this paper, we present the synthesis and a HMBC 1 H- 15 N study of four 2-substituted aminothiazolines. It was observed from HMBC contour plot correlation between five membered ring CH 2 groups with sp 2 nitrogen around 250ppm, while aliphatic hydrogen correlates with sp 3 nitrogen around 90ppm, suggesting that amino form is the major or the unique tautomer present in solution. Theoretical calculations at the M06-2X/cc-pVDZ level were performed and indicated that amino tautomer is slightly more stable (∼1kcalmol −1 ) than imino one.