Ab initio (B3LYP/6-311++G**) calculations have been carried out on the proton transfer of 2H-tetrazole and 5-phenyl-2H-tetrazole with and without the assistance of different nitrogen bases (hydrogen cyanide, ammonia and imidazole). In the absence of base, the proton transfer barrier amounts to 210 kJ mol^{â 1} while in the presence of ammonia it is lowered to 119 kJ mol^{â 1}. Moreover, the inclusion of a solvent cavity of the Onsager type, which increases the first barrier, decreases the second one to 67 kJ mol^{â 1} (for εâ =â 5) which is consistent with experimental data for irbesartan (a 5-aryl-2H-tetrazole derivative).