Calculations by the extended Huckel iteration method with self-consistency with respect to the charges were undertaken for the initial molecule, the radicalanion, and the neutral radical formed during protonation of the latter in 1,3,3-trimethylspiro[indoline-2,2′-(2′H)-chromene]. On the basis of the results from the calculations and analysis of the ESR spectrum of the neutral radical it was concluded that the bond between the spiro carbon atom and the oxygen heteroatom of the pyran ring is not broken during the formation of the radical-anion and its subsequent protonation and that the unpaired electron is delocalized in the π system of the benzopyran fragment of the molecule. Protonation in the radicalanion takes place at the carbon atom at position 3′.