الفهرس 
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Abstract
Theoretical studies on 1,2,4-triazoles favour the 1H-structure 1 for 1,2,4-triazole rather than the more symmetrical 4H-structure 2.These studies suggest that the destabilization of 2 is due to the two contiguous heteroatoms of the same hydridization type1,2. In the gas phase the energy difference between 1 and 2 was 26.3 kJ mol3.Annular prototropic tautomerism of 1,2,4-triazole involves an equilibrium between three possible forms 3a-3c for the unsubstituted 1,2,4-triazoles (R1 = R2 = H the degenerate isomers 3a and 3b are highly preferable energetically compared to 3c4.The theoretical predictions are in accord with the results of photoelectron, IR microwave 5 and X-ray crystal study 6. Regardless of the substituent’s R1 and R2, all Nunsabstituted 1,2,4-triazoles preserve the 1H or 2H structure 3a or 3b7 . In the case of 3-Theoretical studies 9-12 led to conclusion that the unfavorable tautomer 3c has a substantially higher dipole moment than 3a. Which better solubility provided 3c in dipolar solvents and leads to a partial shift of the equilibrium towards it. Thus about 5% of 3c were observed in the 15N NMR spectrum of 1,2,4-triazole13 depending on substituents and solvents.