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Non-empirical calculations using the outer valence Green function (OVGF) approach, which incorporates the main portion of electron correlation and reorganization effects, are reported for the vertical ionization potentials of tria-, penta- and hepta-fulvene, tria-, pentatria-, penta- and heptapenta-fulvalene, spiropentadiene, spiroheptatriene and spirononatetraene. The results provide an overall interpretation of the salient features in the photoelectron spectra.

The three contributions (Fermi-contact, orbital-dipole, and spin-dipole) to the chalcogen-carbon coupling constants of selenophene, tellurophene and a number of their derivatives have been examined by SCF-INDO perturbation theory calculations. All three types of spin-spin interaction are important and, in particular, the direct coupling is controlled by the orbital-dipole and Fermi-contact terms. Correlative arguments and theoretical calculations have been used to predict the sign and order of magnitude of the n J( 33 S 17 O  1 H 13 C ) coupling contants of the congener systems thiophene and furan.

Electric dipole moments have been determined in benzene at 25 and 45 °C for bis(5-nitro-2-pyridyl) sulphide (compound 1) and 2-pyridyl-(5-nitro-2-pyridyl) sulphide (compound 2) and interpreted in terms of molecular conformations. It was found that compound 1 exists in an equilibrium mixture of three twisted conformers (± 36 ° out of the CSC plane), which corresponds to the N,N-inside; N,N-outside; N-inside, N-outside; orientations of the pyridine rings. The analysis for compound 2 suggests that a single skew conformation, where the pyNO 2 group lies on the CSC plane with the N atom inside, exists in solution.

Nonempirical calculations using the equations-of-motion approach, which includes the main portion of electron correlation effects, are reported for the one-bond coupling constants in the three-membered rings borirane, cyclopropane, azirane, oxirane, silirane, phosphirane, and thiirane and related double-bond analogs. The important overall result is that the 1 J (CC) and 1 J (CC) constants are spread over broad ranges, much wider in the case of the double-bond species, with a nearly regular increase with the electronegativity of the central heteroatom. For the boron cycles the smallest 1 J (CC)'s are predicted, with 1 J (CC) surprisingly lower than 1 J (CC). This exceptional pattern is accounted for in terms of the peculiar electronic structure of these rings formed by the electron-deficient B atom. The 1 J (Heteroatom-C), 1 J (Heteroatom-H) and 1 J (CH) couplings correlate correctly with the available experimental data.

In this paper we document the possible performances of the equations‐of‐motion method for predicting second‐order magnetic properties (indirect nuclear spin–spin coupling tensors, nuclear screening tensors, and magnetic susceptibilities). Nonempirical calculations for a series of molecules containing conjugated or cumulated multiple bonds and most of them suffering from UHF triplet instability are reported. In spite of the limitation of the 631G** basis set used, the results fit reasonably well with the main features of the experimental data in all cases but some geminal J’s and the σ’s in diacetylene. Inclusion of the (2p‐2h) interactions brings the theoretical results to a closer agreement with observation. Effects of electron correlation at (1p‐1h) and (1p‐1h) +(2p‐2h) levels of approximation are analyzed by comparison with corresponding results obtained by standard CHF procedures. They are found to be of remarkable importance for the paramagnetic component of σ and χ and for the Fermi‐contact contribu...

The three contributions (Fermi-contact, orbital-dipole, and spin-dipole) to the chalcogen-carbon coupling constants of selenophene, tellurophene and a number of their derivatives have been examined by SCF-INDO perturbation theory calculations. All three types of spin-spin interaction are important and, in particular, the direct coupling is controlled by the orbital-dipole and Fermi-contact terms. Correlative arguments and theoretical calculations have been used to predict the sign and order of magnitude of the n J( 33 S 17 O  1 H 13 C ) coupling contants of the congener systems thiophene and furan.

In this paper we document the possible performances of the equations‐of‐motion method for predicting second‐order magnetic properties (indirect nuclear spin–spin coupling tensors, nuclear screening tensors, and magnetic susceptibilities). Nonempirical calculations for a series of molecules containing conjugated or cumulated multiple bonds and most of them suffering from UHF triplet instability are reported. In spite of the limitation of the 631G** basis set used, the results fit reasonably well with the main features of the experimental data in all cases but some geminal J’s and the σ’s in diacetylene. Inclusion of the (2p‐2h) interactions brings the theoretical results to a closer agreement with observation. Effects of electron correlation at (1p‐1h) and (1p‐1h) +(2p‐2h) levels of approximation are analyzed by comparison with corresponding results obtained by standard CHF procedures. They are found to be of remarkable importance for the paramagnetic component of σ and χ and for the Fermi‐contact contribu...

Ab initio many-body calculations according to Cederbaum's OVGF formalism have been carried out on the IEs of the outer valence orbitals of the cyclopropene analogues, borirene, azirene, oxirene, silirene, phosphirene and thiirene. The internal correlation diagrams and comparison of the theoretical predictions with the experimental values available for the parent single-bond compounds and open-chain dimethyl analogues indicate a complex non-uniform role exerted by the bridgehead heteroatom in this series of highly strained heterocyclopropenes.