TY - JOUR
T1 - Magnetically induced current densities in aromatic, antiaromatic, homoaromatic, and nonaromatic hydrocarbons
AU - Fliegl, Heike
AU - Sundholm, Dage
AU - Taubert, Stefan
AU - Juselius, Jonas
AU - Klopper, Wim
PY - 2009
Y1 - 2009
N2 - "The magnetically induced current densities for ring-shaped hydrocarbons are studied at the density functional theory (DFT) and second-order Moller-Plesset (MP2) levels using gauge-including atomic orbitals. The current densities are calculated using the gauge-including magnetically induced current approach. The calculations show that all studied hydrocarbon rings sustain strong diatropic and paratropic ring currents when exposed to an external magnetic field, regardless whether they are unsaturated or not. For nonaromatic rings, the strength of the paratropic current flowing inside the ring is as large as the diatropic one circling outside it, yielding a vanishing net ring current. For aromatic molecules, the diatropic current on the outside of the ring is much stronger than the paratropic one inside, giving rise to the net diatropic ring current that is typical for aromatic molecules. For antiaromatic molecules, the paratropic ring-current contribution inside the ring dominates. For homoaromatic molecules, the diatropic current circles at the periphery of the ring. The ring current is split at the CH2 moiety; the main fraction of the current flow passes outside the CH, at the hydrogens, and some current flows inside the carbon atom. The diatropic current does not take the through-space short-cut pathway, whereas the paratropic current does take that route. Calculations of the ring-current profile show that the ring current of benzene is not transported by the pi electrons on both sides of the molecular ring. The strongest diatropic ring current flows on the outside of the ring and in the ring plane. A weaker paratropic current circles inside the ring with the largest current density in the ring plane. Due to the ring strain, small unconjugated and saturated hydrocarbon rings sustain a strong ring current which could be called ring-strain current. Nuclear magnetic shieldings calculated for 1,3,5-cycloheptatriene and homotropylium at the DFT and MP2 levels agree well with experimental values."
AB - "The magnetically induced current densities for ring-shaped hydrocarbons are studied at the density functional theory (DFT) and second-order Moller-Plesset (MP2) levels using gauge-including atomic orbitals. The current densities are calculated using the gauge-including magnetically induced current approach. The calculations show that all studied hydrocarbon rings sustain strong diatropic and paratropic ring currents when exposed to an external magnetic field, regardless whether they are unsaturated or not. For nonaromatic rings, the strength of the paratropic current flowing inside the ring is as large as the diatropic one circling outside it, yielding a vanishing net ring current. For aromatic molecules, the diatropic current on the outside of the ring is much stronger than the paratropic one inside, giving rise to the net diatropic ring current that is typical for aromatic molecules. For antiaromatic molecules, the paratropic ring-current contribution inside the ring dominates. For homoaromatic molecules, the diatropic current circles at the periphery of the ring. The ring current is split at the CH2 moiety; the main fraction of the current flow passes outside the CH, at the hydrogens, and some current flows inside the carbon atom. The diatropic current does not take the through-space short-cut pathway, whereas the paratropic current does take that route. Calculations of the ring-current profile show that the ring current of benzene is not transported by the pi electrons on both sides of the molecular ring. The strongest diatropic ring current flows on the outside of the ring and in the ring plane. A weaker paratropic current circles inside the ring with the largest current density in the ring plane. Due to the ring strain, small unconjugated and saturated hydrocarbon rings sustain a strong ring current which could be called ring-strain current. Nuclear magnetic shieldings calculated for 1,3,5-cycloheptatriene and homotropylium at the DFT and MP2 levels agree well with experimental values."
KW - NMR CHEMICAL-SHIFTS
KW - INCLUDING ATOMIC ORBITALS
KW - ZETA VALENCE QUALITY
KW - GAUSSIAN-BASIS SETS
KW - RING CURRENTS
KW - PERTURBATION-THEORY
KW - EFFICIENT IMPLEMENTATION
KW - HOMOTROPENYLIUM CATION
KW - WORKSTATION COMPUTERS
KW - 3-MEMBERED RINGS
KW - 116 Chemical sciences
U2 - 10.1021/jp9029776
DO - 10.1021/jp9029776
M3 - Article
SN - 1089-5639
VL - 113
SP - 8668
EP - 8676
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 30
ER -