Aromaticity, π-electron delocalization, and ring currents

2007 ◽  
Vol 79 (6) ◽  
pp. 969-979 ◽  
Author(s):  
Patrick W. Fowler ◽  
Mark Lillington ◽  
Leif P. Olson
Keyword(s):  
Current Density ◽  
Vector Potential ◽  
Ring Current ◽  
Computational Cost ◽  
Electron Delocalization ◽  
Induced Current ◽  
Simple Interpretation ◽  
Cyclic System ◽  
Ring Currents ◽  
Highest Occupied Molecular Orbital

The magnetic criterion of aromaticity is based on the ability of a cyclic system to support a ring current. If the ring current has the diatropic sense, the system is aromatic; if the sense is paratropic, the system is antiaromatic. Attribution of aromaticity ab initio therefore reduces to the calculation and visualization of induced current density. This can be achieved at modest computational cost within the ipsocentric approach, where current density at any point in space is calculated with that point as origin of vector potential. This choice leads to accurate maps of current density and a uniquely simple interpretation in terms of nonredundant orbital contributions governed by translational and rotational selection rules. For example, four-electron diatropicity and two-electron paratropicity are predicted for delocalized forms of [4n+2]- and [4n]-annulenes, respectively. A new application to homoaromatic systems is described. Two model tris-homoaromatics, both neutral molecules, are shown to exhibit a through-space, highest occupied molecular orbital (HOMO)-dominated, four-electron ring current, in a direct analogy with the conventional "aromatic" benzene π-current.

scholarly journals Magnetically induced ring currents in naphthalene-fused heteroporphyrinoids

2021 ◽  
Author(s):  
Markus Rauhalahti ◽  
D Sundholm ◽  
Mikael P. Johansson
Keyword(s):  
Current Density ◽  
Quantum Chemical ◽  
Ring Current ◽  
Induced Current ◽  
Ring Currents ◽  
Induced Currents

The magnetically induced current density of an intriguing naphthalene-fused heteroporphyrin have been studied, using the quantum-chemical, gauge-including magnetically induced currents (GIMIC) method. The ring-current strengths and current-density pathways for the...

scholarly journals Magnetically induced ring currents in metallocenothiaporphyrins

2021 ◽  
Author(s):  
Rashid R. Valiev ◽  
Theo Kurtén ◽  
Lenara Valiulina ◽  
Sergey Yu. Ketkov ◽  
Victor Cherepanov ◽  
...  
Keyword(s):  
Current Density ◽  
Triplet States ◽  
Induced Current ◽  
Susceptibility Tensor ◽  
Ring Currents ◽  
Singlet And Triplet States

The magnetically induced current-density susceptibility tensor (CDT) of the lowest singlet and triplet states of the metallocenothiaporphyrins, where the metal is V, Cr, Mn, Fe, Co, Ni, Mo, Tc, Ru,...

scholarly journals (4n +2)π Huckel’s rule of Bn NnC(8-2n) H8 as anti-cancer heterocyclic systems

2020 ◽  
Vol 11 (29) ◽  
pp. 129-150
Author(s):  
Neda SamieiSoofi ◽  
Majid Monajjemi
Keyword(s):  
Aromatic Ring ◽  
Current Density ◽  
Ring Current ◽  
Ring Currents ◽  
Anti Cancer ◽  
Whole Space ◽  
Homo And Lumo ◽  
Localized Orbital ◽  
Homo Lumo ◽  
Magnetic Mechanism

Replacing of Boron and nitrogen atoms in [8] annulene molecule help us for explaining the details of mentioned magnetic mechanism concerning the ring currents of the carbon disappearing in the isoelectronic azabora-hetero-cycles variants (Bn Nn C(8-2n) H82-,n=0,1,2,3 and4 The (4n+2)π systems aromatic on variants of BnNnC(8-2n) H8 (n=0, 1 ,2,3 and 4) via the localized orbital by considering the current density induced have been studied. It has been predicted a four-electron dia-tropic (aromatic) ring current for (4n+2) π aza-bora-hetero-cycles variants of BnNnC (8-2n) H8(n=0,1 ,2,4) and a two-electron para-tropic (anti-aromatic) current for (4n) π. HOMO and LUMO energies and also HOMO/LUMO overlapping in whole space have been calculated. Two forms can be considered, first the HOMO–LUMO transition leads to a para-tropic contribution, and second HOMO–LUMO+1 transitions to the dia-tropic contributions. In addition, the NICS and SNICS values confirm the amounts of aromaticity and anti-aromaticity in those rings.

scholarly journals The B2 Structural Motif as a Tool for Modulating Ring Currents in Monocyclic Li Clusters

Chemistry ◽  
2021 ◽  
Vol 3 (3) ◽  
pp. 1063-1073
Author(s):  
Slađana Đorđević ◽  
Slavko Radenković
Keyword(s):  
Current Density ◽  
Structural Motif ◽  
Induced Current ◽  
Continuous Transformation ◽  
Structural Modifications ◽  
Ring Currents ◽  
Current Densities

Magnetically induced current densities, calculated at the M06-2X/def2-TZVP level using the diamagnetic-zero version of the continuous transformation of origin of current density (CTOCD-DZ) method, were employed to study the aromaticity in Li3B2− and Li4B2. It was found that the Li3/Li4 rings in Li3B2− and Li4B2 remarkably resemble the monocyclic Li3+ and Li42+ clusters. Unlike the parent Li3+ and Li42+ systems that sustain negligibly weak global current density circulation, the Li3B2− and Li4B2 clusters exhibit a strong diatropic current density. The present work demonstrates how structural modifications introduced by the B2 unit can be used for modulating the current density in cyclic Li-based clusters.

A study on the aromaticity and ring currents of dithienopyridines and dithienobenzene

2018 ◽  
Vol 17 (01) ◽  
pp. 1850006
Author(s):  
Bi Xiao Yun ◽  
Ablikim Kerim
Keyword(s):  
Ring Current ◽  
Resonance Energy ◽  
Ring Structure ◽  
Electron Delocalization ◽  
Aromaticity Index ◽  
Ring Currents ◽  
Middle Ring ◽  
Topological Resonance Energy ◽  
Local Aromaticity

The global aromaticity of dithienopyridine and dithienobenzene isomers was investigated using the topological resonance energy (TRE) and percentage topological resonance energy (%TRE) methods. The effect of variations in the positions of sulfur and nitrogen atoms on [Formula: see text]-electron delocalization is analyzed. The local aromaticity of these isomers is described based on the bond resonance energy (BRE) and circuit resonance energy (CRE) methods. Our BRE and CRE results show that structure of the central six-membered rings has a strong effect on global aromaticity. The aromaticity of these dithienopyridine isomers is enhanced when a complete pyridine unit exists in their middle ring structure, while the aromaticity of the dithienobenzene isomers is enhanced when a complete benzene unit exists in their middle ring structure. For dithienopyridines, our results obtained using the TRE method correlate well with the Bird aromaticity index as reported in the literature. Our ring-current results show that all these compounds are diatropic systems.

scholarly journals The Magnetic Response of Starphenes

Chemistry ◽  
2021 ◽  
Vol 3 (4) ◽  
pp. 1381-1391
Author(s):  
Mesías Orozco-Ic ◽  
Gabriel Merino
Keyword(s):  
Magnetic Field ◽  
External Magnetic Field ◽  
Current Density ◽  
Magnetic Response ◽  
Induced Current ◽  
Induced Magnetic Field ◽  
Ring Currents

The aromaticity of [n]starphenes (n = 1, 4, 7, 10, 13, 16), as well as starphene-based [19]dendriphene, is addressed by calculating the magnetically induced current density and the induced magnetic field, using the pseudo-π model. When an external magnetic field is applied, these systems create diatropic currents that split into a global peripheral current surrounding the starphene skeleton and several local currents in the acene-based arms, resulting in large shielding cones above the arms. In particular, the arm currents are smaller than their linear analogs, and in general, the strengths of the ring currents tend to weaken as the starphene get larger.

Coherent Ring Currents in Chiral Aromatic Molecules Induced by Linearly Polarized UV Laser Pulses

2013 ◽  
Vol 543 ◽  
pp. 381-384 ◽  
Author(s):  
Manabu Kanno ◽  
Hirohiko Koho ◽  
Hirobumi Mineo ◽  
Sheng Hsien Lin ◽  
Yuichi Fujimura
Keyword(s):  
Aromatic Ring ◽  
Quantum Dynamics ◽  
Ring Current ◽  
Molecular System ◽  
Laser Pulses ◽  
Uv Laser ◽  
Aromatic Molecules ◽  
Ring Currents ◽  
Linearly Polarized ◽  
Coherent Ring

In recent years, laser control of electrons in molecular system and condensed matter has attracted considerable attention with rapid progress in laser science and technology [. In particular, control of π-electron rotation in photo-induced chiral aromatic molecules has potential utility to the next-generation ultrafast switching devices. In this paper, we present a fundamental principle of generation of ultrafast coherent ring currents and the control in photo-induced aromatic molecules. This is based on quantum dynamics simulations of π-electron rotations and preparation of unidirectional angular momentum by ultrashort UV laser pulses properly designed. For this purpose, we adopt 2,5-dichloro [(3,6) pyrazinophane (DCPH) fixed on a surface, which is a real chiral aromatic molecule with plane chirality. Here π electrons can be rotated along the aromatic ring clockwise or counterclockwise by irradiation of a linearly polarized laser pulse with the properly designed photon polarization direction and the coherent ring current with the definite direction along the aromatic ring is prepared. This is contrast to ordinary ring current in an achiral aromatic ring molecule with degenerate electronic excited state, which is prepared by a circularly polarized laser [2]. In this case, π electrons rotate along the Z-axis of the laboratory coordinates, while for the present case electrons rotate along the z-axis in molecular Cartesian coordinates. It should be noted that signals originated from the coherent ring currents prepared by linearly polarized ultrashort UV lasers are specific to the chiral molecule of interest.

scholarly journals The distribution of the ring current: Cluster observations

2011 ◽  
Vol 29 (9) ◽  
pp. 1655-1662 ◽  
Author(s):  
Q.-H. Zhang ◽  
M. W. Dunlop ◽  
M. Lockwood ◽  
R. Holme ◽  
Y. Kamide ◽  
...  
Keyword(s):  
Current Density ◽  
Ring Current ◽  
Local Times ◽  
Distribution Profile ◽  
Full Circle ◽  
Equatorial Current ◽  
The Mean ◽  
Current Flows ◽  
First Time

Abstract. Extending previous studies, a full-circle investigation of the ring current has been made using Cluster 4-spacecraft observations near perigee, at times when the Cluster array had relatively small separations and nearly regular tetrahedral configurations, and when the Dst index was greater than −30 nT (non-storm conditions). These observations result in direct estimations of the near equatorial current density at all magnetic local times (MLT) for the first time and with sufficient accuracy, for the following observations. The results confirm that the ring current flows westward and show that the in situ average measured current density (sampled in the radial range accessed by Cluster ~4–4.5 RE) is asymmetric in MLT, ranging from 9 to 27 nA m−2. The direction of current is shown to be very well ordered for the whole range of MLT. Both of these results are in line with previous studies on partial ring extent. The magnitude of the current density, however, reveals a distinct asymmetry: growing from 10 to 27 nA m−2 as azimuth reduces from about 12:00 MLT to 03:00 and falling from 20 to 10 nA m−2 less steadily as azimuth reduces from 24:00 to 12:00 MLT. This result has not been reported before and we suggest it could reflect a number of effects. Firstly, we argue it is consistent with the operation of region-2 field aligned-currents (FACs), which are expected to flow upward into the ring current around 09:00 MLT and downward out of the ring current around 14:00 MLT. Secondly, we note that it is also consistent with a possible asymmetry in the radial distribution profile of current density (resulting in higher peak at ~4–4.5 RE). We note that part of the enhanced current could reflect an increase in the mean AE activity (during the periods in which Cluster samples those MLT).

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