Aromaticity of anthranil and its isomers, 1,2-benzisoxazole and benzoxazole

Direct computation of the π-current density, that is, the ‘ring current’, of anthranil (1) and its isomers 1,2-benzisoxazole (2) and benzoxazole (3) reveals different patterns of current flow: isomers 2 and 3 sustain strong benzene-like currents in the six-membered and bifurcated flow in the five-membered ring, whereas, in keeping with its lower thermodynamic stability, 1 has only a perimeter circulation without separate monocycle currents. Although the ring current criterion does not offer a sharp distinction between 2 and 3, their difference in thermodynamic stability is identical to that between isoxazole (4) and oxazole (5) suggesting an aromaticity order 1 < 2 ≈ 3.