Kerr constants, Cotton–Mouton constants, and magnetic anisotropies of pyridazine, pyrimidine, and pyrazine

Abstract

Experimental dipole moments, molar Kerr constants, and molar Cotton–Mouton constants obtained at 298 K and 633 nm are reported for pyridazine, pyrimidine, and pyrazine as solutes in dioxan and cyclohexane. Analysis of the Kerr-effect data yielded the effective polarisability anisotropies, which were then used to evaluate the molecular magnetic anisotropies from the Cotton–Mouton constants. The magnetic criterion of aromaticity was applied by estimating for each diazine the non-local contribution to the out-of-plane component of the magnetisability. Progressive replacement of –CH by –N causes a considerable reduction inelectron delocalisation and, by inference, aromaticity in the order benzene > pyridine ≈ pyridazine ≈ pyrazine > pyrimidine > s-triazine.