Rosario G. Viglione

Why Downfield Proton Chemical Shifts Are Not Reliable Aromaticity Indicators

Traces of magnetizability, traces of magnetic shielding at the hydrogen nuclei, and nucleus-independent chemical shift are not reliable aromaticity quantifiers for planar conjugated hydrocarbons. A measure of aromaticity is provided by the out-of-plane tensor components, whose magnitude is influenced by the pi-ring currents. The failure of nucleus-independent chemical shift in this regard was proved for the molecule shown in the abstract graphic, sustaining a diatropic pi-current. The validity of the ring-current model is reaffirmed. [structure: see text]

Calculation of the gas phase specific rotation of (S)-propylene oxide at 355 nm

Abstract The experimental gas phase specific rotation of ( S )-propylene oxide at 355 nm is correctly predicted at the DFT/B3LYP level of theory only adopting fairly large basis sets, such as aug-cc-pVTZ and aug-cc-pVQZ, or, alternatively, the much smaller polarizability-consistent Sadlej basis set. Therefore, considering also the sensitivity to solvent effects, this small and rigid molecule, which has been considered an ideal test case for theoretical investigations, is, on the contrary, one of the most difficult cases to be treated.

THE DECOHERENCE CRITERION

The decoherence mechanism signals the limits beyond which the system dynamics approaches the classical behavior. We show that in some cases decoherence may also signal the limits beyond which the system dynamics has to be described by quantum field theory, rather than by quantum mechanics.

Structure, ring currents and magnetic properties of 12b, 12d, 12f-triaza-12c, 12e, 12g-tribora-coronene

Abstract The title molecule (TTC), formally derived by replacing the inner C6 ring of coronene with (BN)3, is predicted at MP2/6-31G* and B3LYP/6-31G* levels to have a planar D3h equilibrium structure. Coupled Hartree–Fock calculations on TTC with the distributed-gauge continuous transformation of current density-diamagnetic zero (CTOCD-DZ) method predict a strongly diatropic coronene-like perimeter ring current, but with localized inner borazine-like diatropic circulations replacing the central paramagnetic circulation of coronene. On magnetic criteria, therefore, TTC is predicted to be at least as aromatic as coronene.

Ring currents and magnetic properties of C48N12 dodecaaza[60-S6]fullerenes

The continuous transformation of the origin of the current density (CTOCD) method has been employed, at the ab initio CHF level of theory and adopting a medium size ad hoc polarized basis set, to predict fairly accurate, origin-independent magnetic properties for the two dodecaaza[60-S6]fullerene isomers. The results show that the two isomers have a very different magnetic behavior, the thermodynamically less stable isomer (I) being characterized by paratropic π-electron ring currents, which largely reduce the overall molecular diamagnetism, and, on the contrary, the more stable isomer (II) characterized by diatropic π-electron ring currents flowing on the external hexagons of each triphenylene-type unit. However, on the basis of the computed magnetizability and central magnetic shielding, II is found to be no more aromatic than fullerene C60. Computed 13C and 15N magnetic shieldings of both isomers are reported, which might be useful for identification purposes.