The diamagnetic susceptibilities of hinokitiol ((β-thujaplicin) and α-thujaplicin in powdered crystal form have been measured and the structures of the tropolone-ring are discussed. The observed molar susceptibilities obtained in the present experiments are -(102±1)×10 for hinokitiol, -(100±3)×10 for α-thujaplicin (colourless, m. p. 34°), and -(97±2)×10 for α-thujaplicin (light yellow, m. p. 24°). These observed data have been compared with calculated values, which were computed by use of the four methods ; the Pascal\u27s additive law, the Slater-Angus method, Langevin\u27s formula referring to the diamagnetism for the planar orbit, and the theory of diamagnetic anisotropy of molecular orbitals (London\u27s method), with the result that there are six π-electrons, within each tropolone-ring of these compounds, which are able to revolve along the closed circuit constructed out of the periphery of seven membered ring. As a necessary consequence of this condition, it follows the ionization between one of the carbon atoms in the ring system and the oxygen atom in the carbonyl group, assuming the former a positive charge and the later a negative one
