Pyrazole is a five-membered aromatic ring containing two adjacent nitrogens. The pyrrole-type nitrogen with a lone pair of electrons involved in aromaticity of the pyrazole ring. The other pyridine-type sp2-hybridized nitrogen has its lone pair away and out of the plane from the ring structure . Hence the preferential protonation of pyrazole would be at N(2)-nitrogen. The resonance structures of protonated pyrazole (pyrazolium cation) are shown in scheme 1.