Angelo Mangini

D-orbital effects and the structure of the alpha-thiocarbanion

Improved computational results show that sulfur-3d orbital effects are essential for the proper description of the bonding in the alpha-thiocarbanions −CH2SH and −CH2SCH3. The nature of the d-orbital effects has been analyzed, and reasons for the earlier failures to fine these effects have been determined.

Quantitative orbital analysis of ab initio SCFMO computations: Part II. Conformational preferences in H2NOH and H2NSH

Abstract The results obtained in a quantitative orbital analysis of the ab initio SCFMO computations performed on hydroxylamine and thiohydroxylamine are described. The analysis is based on the use of fragment localized MOs and the energy effects associated with their interactions are estimated, in the framework of the ab initio SCF—MO computations, using PMO expressions. In particular the factors are analyzed which control the conformational preference in these molecules, and the effect of the sulphur 3d orbitals upon conformational stability is discussed.

A comparative theoretical study of the effects of first- and second-row substituents in α-substituted carbanions

This Paper reports the investigations we carried out on substituent effects in the carbanions H2–X (where X = F, Cl, OH, or SH), using an ab initio SCF-MO treatment with three different basis sets of at least double zeta quality augmented with a set of diffuse p functions on carbon and with or without diffuse p functions and d polarization functions on the heteroatoms It was found that with all these substituents the carbanion centre is pyramidal, with inversion barriers that are larger than that of H3, and which decrease in the order Cl > F > OH > SH. We also found that the order of stabilization energies is Cl > SH > F > OH. The 3d orbitals play a negligible role in determining the stabilization energies of H2–Cl and H2–SH. However, the 3d orbitals have a significant effect on the determination of some structural properties of H2–SH and H2–Cl.

CONFORMATIONAL DEPENDENCE OF THE ELECTRON ACCEPTOR CHARACTER OF ALKYLTHIOGROUPS IN ORGANIC RADICALS

Abstract We have found that in the radical anions and nitroxides from p-alkylthionitrobenzenes, the alkylthiogroups behave as electron-withdrawing substituents and that their electron-acceptor character increases along the series methyl, ethyl, t-butyl. This behaviour could be explained in terms of a change of conformation of the SR substituent. Actually the ESR spectra of the radicals from the following isotopically substituted derivatives, show very different hyperfine splitting constants at the 13C: large and practically temperature independent in the case of the t-butylthionitrobenzene (II), and much smaller and strongly dependent on temperature with the methylthio analog (I). This finding provides evidence that in the latter derivative the methyl group deviates slightly from coplanarity with the aromatic ring, while the more stable conformation of (II) is that one placing the t-butyl group above the molecular plane with the Cp-S-13C plane perpendicular to the aromatic system.