NAPHTHO[1,8-C,D-4,5-C',D']BIS[1,2,6]SELENADIAZINE

The synthesis and chemical and physical properties of the title compound (1) are reported. With one notable exception the spectroscopic properties of naphtho[1, 8-c, d:4, 5-c', d'] bis[1, 2, 6] selenadiazine (1) closely resemble those observed for naphtho[1, 8-c, d:4, 5-c', d'] bis[1, 2, 6]thiadiazine (2). In particular, the compounds show 1HNMR chemical shifts of δ 5.91 (1) and 4.74 (2) in dimethyl-d6 sulfoxide. The discrepancy in the 1HNMR chemical shifts of 1 and 2 is ascribed to differences in the magnitude of the induced paramagnetic ring currents. Theoretical analysis of these results leads to two important conclusions: (1) The magnitude of paramagnetic ring currents in structurally similar molecules is primarily determined by the spectrum of orbital energies and, in particular, the HOMO-LUMO energy gap. (2) The difference between the nitrogen-chalcogen resonance integrals in 1 and 2 is the dominant factor in determining the relative magnitude of the HOMO-LUMO energy gaps (and thus the intensity of the paramagnetic ring currents). Evidence is presented to show that the most important excitation for the development of the paramagnetic ring current in 1 and 2 is from the HOMO (B1u) to the LUMO (Au), whereas the long-wavelength band in the electronic spectrum involves the HOMO (B1u) → second LUMO (B2g) transition. © 1979, American Chemical Society. All rights reserved.