Reactivities and structures of compounds of the thiophene and furan series bearing electron-acceptor substituents

The experimental data on orientation in electrophilic substitution reactions of compounds of the furan and thiophene series that bear electron-acceptor substituents were examined. Within the framework of the CNDO/2 method, the electronic structures, dipole moments, and spin-spin coupling constants in the PMR spectra were calculated for model systems — 2-formylthiophene, furfural, and their oxygen-protonated forms. The results of the calculations are compared with the available experimental data on the dipole moments and spin-spin coupling constants, which made it possible to discuss the geometrical structures of the compounds. An analysis of data on the chemical behavior of these compounds demonstrated that, in contrast to the charges found using the -electron approximation, the total charges on the atoms calculated by the CNDO/2 method are rather effective indexes of the reactivity.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 155–164, February, 1972.