Effect of the nature of the heteroatoms in the spiro group on the structure of spiropyrans and an x-ray study of spiropyran of the dithiolane series C17H16O2S2

Conclusions We have carried out an x-ray diffraction study of tetramethylenespiro[1,3-dithiolane-2,7[7H]-furo[3,2-f]-[2H -1]-benzopyran], containing the three heteroatoms S, S, O in the spiro group. The orbital n-* interactions virtually do not affect the bond lengths in the spiro group of the molecule; therefore the C_spiro-O bond, which is ruptured upon photoexcitation, remains unlengthened in the ground state. The differences in the lengths of the chemically equivalent C_spiro-S bonds are due to electrostatic repulsions of the unshared electron pairs of the heteroatoms S and O, which have different relative orientation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1567–1569, July, 1988.