Half-waves (E1/2) of polarogram of some aromatic ketones were measured. By use of the simple HMO, it was found that the lowest unoccupied MO (LUMO) energy is well correlated with the E1/2. From the correlation between the LUMO energy and the E1/2, the conformation of neutral molecules of some thermochromic ethylenes in solution and the origin of conformational change were estimated.
