A computational approach to intermolecular proton transfer in the solid state: assistance by proton acceptor molecules

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(-1) while in the presence of ammonia it is lowered to 119 kJ mol(-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(-1) (for epsilon = 5) which is consistent with experimental data for irbesartan (a 5-aryl-2H-tetrazole derivative).