2,2'-Dithiobispyrazine: about the disulfide bond.

X-ray diffraction studies reveal that pyrazine-2-thiol undergoes condensation to 2,2'-dithiobispyrazine [systematic name: 2-(pyrazin-2-yldisulfanyl)pyrazine], CHNS (I), under aerial conditions. In the molecule of I, the pyrazine rings are arranged in an almost perpendicular manner, with an absolute value of the C-S-S-C torsion angle of -91.45 (6)°. A search in the Cambridge Structural Database confirmed that such a conformation is typical for disulfide compounds. Three different rotamers of disulfide I were studied using quantum theoretical studies. The rotamer of lowest energy was observed in the crystalline state in the structure stabilized by hydrogen-bond, chalcogen-bond and stacking interactions. Further quantum chemical computations confirm that 2,2'-dithiobispyrazine can react according to the S2 mechanism.