Abstract: 2, 7-Methanothia [9] annulene (1) was synthesized from 1, 6-diiodo-1, 3, 5- cycloheptatriene in 13 steps. Variabletemperature" C NMR and electronic spectra indicated that 1 is in equilibrium with its valence isomer, 9-thiatricyclo-[4.3. 1.01~ 6] deca-2, 4, 7-triene (2). From the I3C NMR spectra, the equilibrium ratio 1/2 was estimated as 16/84 in CDC13- CS2 (1: l) at 30 OC. Comparison of the temperature dependence of I3C chemical shifts of ...