Basicity of N-H and N-Methyl-1,2,3-triazoles in the Gas Phase, Solution and Solid State: An Experimental and Theoretical Study.
The gas-phase and aqueous basicities of six 1,2,3-triazoles have been determined, the former by FT-ICR and the latter by spectrophotometry and 1H NMR. The gas-phase experiments agree very well with the Gibbs free energies calculated at the B3LYP/6-31G* level. In contrast, only semiquantitative ascertainments are possible when basicities in the gas phase and in solution are compared. It is possible, with the aid of calculations, to obtain a complete picture of the complex equilibria involved in C-substituted N-H-1,2,3-triazoles. The crystal structures of 4(5)-phenyl-1,2,3-triazole (4) and 4(5)-nitro-1,2,3-triazole (15) have been determined. In the gas phase, 2Htautomers b always predominate, while in aqueous solution, both 1H and 2H tautomers − a and b − are present. Finally, in the solid state,1 exists as a 1:1 mixture of 1a and 1b, while 4 is in the 4b tautomeric form and 15 is a 1H tautomer 15a. These conclusions − a in the gas phase, a + b in solution, and equal probabilities of finding either a or b in the crystal − are probably general for all 1,2,3-triazoles.