Concurrence between Current Density, Nucleus-Independent Chemical Shifts, and Aromatic Stabilization Energy: The Case of Isomeric [4]- and [5]Phenylenes

2013 ◽  
Vol 78 (15) ◽  
pp. 7544-7553 ◽  
Author(s):  
Renana Gershoni-Poranne ◽  
Christopher M. Gibson ◽  
Patrick W. Fowler ◽  
Amnon Stanger
Keyword(s):  
Current Density ◽  
Chemical Shifts ◽  
Stabilization Energy ◽  
Aromatic Stabilization

CC/B–N substitution in five membered heterocycles. A computational analysis

2017 ◽  
Vol 41 (9) ◽  
pp. 3619-3633 ◽  
Author(s):  
Vaibhav A. Dixit ◽  
William R. F. Goundry ◽  
Simone Tomasi
Keyword(s):  
Computational Analysis ◽  
Stabilization Energy ◽  
Stabilization Energies ◽  
Neutral Conditions ◽  
Aromatic Stabilization

Novel five-membered azaboroles are aromatic, stable under neutral conditions, isomer stabilization energy is explained using σ-bond and aromatic stabilization energies.

scholarly journals Relativity or aromaticity? A first-principles perspective of chemical shifts in osmabenzene and osmapentalene derivatives

2020 ◽  
Vol 22 (19) ◽  
pp. 10863-10869 ◽  
Author(s):  
Cina Foroutan-Nejad ◽  
Jan Vícha ◽  
Abhik Ghosh
Keyword(s):  
Current Density ◽  
First Principles ◽  
Chemical Shifts ◽  
Induced Current ◽  
Aromatic System ◽  
System P

The topology of the magnetically induced current density in osmabenzene suggests that the molecule is a novel type of Craig–Möbius aromatic system.

scholarly journals Synthesis of a Highly Aromatic and Planar [10]Annulene

2021 ◽  
Author(s):  
Karnjit Parmar ◽  
Christa S. Blaquiere ◽  
Brianna Lukan ◽  
Sydnie Gengler ◽  
Michel Gravel
Keyword(s):  
Stabilization Energy ◽  
Alternative Strategy ◽  
Ring Size ◽  
Ring Strain ◽  
Aromatic Structure ◽  
Close Proximity ◽  
Ring Interaction ◽  
Aromatic Stabilization

As the next neutral structure following Hückels rule, a planar and aromatic [10]annulene is ideal to study the link between ring size and aromaticity. However, the puckered geometry of the parent [10]annulene suggests that the aromatic stabilization energy is not sufficient to overcome the ring strain that exists when the system is forced into planarity. It has been shown computationally that this ring strain can be alleviated through the addition of two or more cyclopropane rings to the periphery, thereby creating theoretically aromatic structures. An alternative strategy to eliminating the issue of ring strain was demonstrated experimentally with the successful preparation of the highly aromatic 1,6-didehydro[10]annulene. However, the system rapidly cyclizes at -40°C to a naphthalene diradical due to the close proximity of the in-plane p-orbitals present in the system. Here we show that cyclopropanating one side of the unstable annulene successfully prevents the destabilizing cross-ring interaction while maintaining a highly aromatic structure. Remarkably, the formed [10]annulene is bench stable and can be stored for extended periods of time.<br>

How Much Aromatic Naphthalene and Graphene Are?

2018 ◽  
Author(s):  
Vaibhav Dixit ◽  
Yashita Y. Singh
Keyword(s):  
Material Science ◽  
Regression Models ◽  
Experimental Validation ◽  
High Reactivity ◽  
Stabilization Energy ◽  
Reference Systems ◽  
Axis Extension ◽  
Molecular Sizes ◽  
Size Estimates ◽  
Aromatic Stabilization

<p>Naphthalene, (Aromatic stabilization Energy; ASE, 50-60 kcal/mol) polyacenes and graphene are considered aromatic. Existing models for polyacenes predict a linearly increasing ASE and give little insights into their high reactivity and decreasing stability. Graphene’s aromaticity has been studied earlier qualitatively suggesting alternate Clar’s sextet and two-electrons per ring, but ASE estimates have not been reported yet. In this paper, various Heat of Hydrogenation (HoH) and isodesmic schemes have been proposed and compared for the estimation of naphthalene ASE. Results show that HoH schemes are simple to design, are equivalent to isodesmic schemes, and unconjugated unsaturated reference systems predict ASE values in agreement with literature reports. Partially aromatic reference systems underestimate ASE. HoH schemes require calculations for a smaller number of structures, and offer scope for experimental validation, and involve enthalpy differences. Polyacene (X-axis extensions of benzene) ASE estimates (using HoH scheme) correlate well with experimental instability data and offer new physical insights explaining the absence of arbitrarily larger polyacenes. ASEs extrapolated from quadratic and logarithmic regression models have been used to estimate the largest polyacene with limiting ASE values. ASE values for Pyrene (Y-axis extension of benzene) and higher analogues (here called pyrene-vertacenes) are estimated using HoH schemes. Further truncated graphene models and graphene are approximated as combinations of polyacene and pyrene-vertacene units. First ever ASE and molecular sizes (22-255 nM) estimates predict nanometer size ranges for flat graphene in agreement with recent experiments and offer new physical insights. These ASE and size estimates for graphene may prove useful in the design of novel energy (hydrogen) storage, electronic and material science applications.</p>

On the σ,π-energy separation of the aromatic stabilization energy of cyclobutadiene

2007 ◽  
Vol 9 (20) ◽  
pp. 2517-2530 ◽  
Author(s):  
Georg Hohlneicher ◽  
Lars Packschies ◽  
Johannes Weber
Keyword(s):  
Stabilization Energy ◽  
Energy Separation ◽  
Aromatic Stabilization

scholarly journals Aromaticities of Five Membered Heterocycles through Dimethyldihydropyrenes Probe by Magnetic and Geometric Criteria

2015 ◽  
Vol 2015 ◽  
pp. 1-11
Author(s):  
Maria ◽  
Khurshid Ayub
Keyword(s):  
Chemical Shifts ◽  
Reference Models ◽  
H Nmr ◽  
Quantitative Estimates ◽  
Shift Analysis ◽  
Structural Criterion ◽  
Stabilization Energies ◽  
Suitable Reference ◽  
Chemical Shift Analysis ◽  
Aromatic Stabilization

Aromaticities of five membered heterocycles, containing up to three heteroatoms, are quantified through the dimethyldihydropyrene (DHP) probe. Bond fixation caused by the fusion of heterocycles to the dimethyldihydropyrene nucleus (DHPN) was measured by changes in the1H NMR chemical shifts (magnetic) and bond lengths alterations (structural criterion). Chemical shifts of dihydropyrenes were calculated at GIAO HF/6-31G(d)//B3LYP/6-31+G(d). For1H NMR chemical shift analysis, two nonaromatic reference models are studied. Among the studied heterocycles, pyrazole and triazole are about 80–85% aromatic relative to benzene, through both magnetic and geometric criteria. Thiazole and oxazoles are found least aromatic where quantitative estimates of aromaticities are about 34–42%, relative to benzene. These quantitative estimates of aromaticities of five membered heterocycles are also comparable to those from aromatic stabilization energies. The quantification of aromaticity through energetic, magnetic, and structural criteria can deliver the similar inferences provided that suitable reference systems are chosen.

scholarly journals Experimental and Theoretical Evidence for Aromatic Stabilization Energy in Large Macrocycles

2021 ◽  
Vol 143 (5) ◽  
pp. 2403-2412
Author(s):  
Michael Jirásek ◽  
Michel Rickhaus ◽  
Lara Tejerina ◽  
Harry L. Anderson
Keyword(s):  
Stabilization Energy ◽  
Theoretical Evidence ◽  
Aromatic Stabilization
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