Quantum chemical investigation of the electronic structure of poly(2,4-dioxocyclobuta-1,3-diylidene)

The electronic structure of poly(2,4-dioxocyclobuta-1,3-diylidene) molecule is calculated by the semiempirical CNDO/S3 method. The calculated Wiberg indices and the additive occupancies of interatomic bonds determine the structural formula, which includes the C=C and C=O conjugated double bonds and corresponds to the name of the compound. Polarization of C=O bonds and πelectron conjugation do not lead to a zwitterionic structure with positive aromatic fourmembered cycles. The indices and occupancies of carboncarbon bonds 1– 3 and 2– 4 are σelectronic, negative, and negligibly small. The band structure corresponds to strong electronaccepting properties of the polymer; the MO of the bottom of the lowlying vacant band contains 2pπorbitals of all atoms of the compound. The occupied π-electronic bands do not overlap, and their widths are relatively small. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 5, pp. 781–786, September–October, 1998.