Tautomeric equilibria and aromaticity of phosphodiazoles: An ab initio study

► We model tautomeric equilibria and aromaticity of all possible phosphodiazoles. ► The relative energy of a tautomer is linearly related to pEDA aromaticity. ► We visualize the lone pairs via 3D maps of Laplacian of electron density. ► We estimate the lone pairs repulsions by Natural Steric Analysis. ► Nitrogen-nitrogen repulsions are stronger than nitrogen-phosphorus.