The electron density of delocalized bonds (EDDBs) as a measure of local and global aromaticity

Szczepanik, Dariusz W.; Solà, Miquel

doi:10.1016/b978-0-12-822723-7.00008-x

Cited by 21 publications

(31 citation statements)

References 56 publications

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“…Isosurfaces (isovalue = 0.4 au) of LOL-π of C 18 -(CO) n (n = 6, 4, and 2).Chemistry-A European JournalSzczepanik et al and recently reviewed in Refs [58,59]. is a powerful and elegant technique for deciphering electron delocalization in chemical systems.…”

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confidence: 99%

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C₁₈) Precursors, C₁₈‐(CO)_n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (‐CO) Groups**

Wang

Liu

Yan

et al. 2021

Chemistry A European J

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The bonding character, electron delocalization, and aromaticity of the cyclo [18]carbon (C 18 ) precursors, C 18 -(CO) n (n = 6, 4, and 2), have been studied by combining quantum chemical calculations and various electronic wavefunction analyses with different physical bases. It was found that C 18 -(CO) n (n = 6, 4, and 2) molecules exhibit alternating long and short CÀ C bonds, and have out-of-plane and in-plane dual π systems (π out and π in ) perpendicular to each other, which are consistent with the relevant characteristics of C 18 . However, the presence of carbonyl (-CO) groups significantly reduced the global electron conjugation of C 18 -(CO) n (n = 6, 4, and 2) compared to C 18 . Specifically, the -CO group largely breaks the extensive delocalization of π in system, and the π out system is also affected by it but to a much lesser extent; as a consequence, C 18 -(CO) n (n = 6, 4, and 2) with larger n shows weaker overall aromaticity. Mostly because of the decreased but still apparent π out electron delocalization in the C 18 -(CO) n (n = 6, 4, and 2), a notable diatropic induced ring current under the action of external magnetic field is observed, demonstrating the clear aromatic characteristic in the molecules. The correlation between C 18 -(CO) n (n = 6, 4, and 2) and C 18 in terms of the gradual elimination of -CO from the precursors showed that the direct elimination of two CO molecules in C 18 -(CO) n (n = 6, 4, and 2) has a synergistic mechanism, but it is kinetically infeasible under normal conditions due to the high energy barrier.

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confidence: 99%

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C₁₈) Precursors, C₁₈‐(CO)_n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (‐CO) Groups**

Wang

Liu

Yan

et al. 2021

Chemistry A European J

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“…Computationally, aromatic delocalization pathways can be observed as currents induced by an external magnetic field using the ACID or GIMIC methods. Current density maps as probes for global and local aromaticity were also presented by Steiner et al [98].The other approach, electron density of delocalized bonds (EDDB) [99][100][101][102], employs a decomposition scheme for electron density. These three computational approaches, applied to porphyrins, give a similar picture of the [18] annulene global delocalization pathway (Figure 8), while the local delocalization does not appear to be so equal.…”

Section: Electron Delocalization Indicesmentioning

confidence: 99%

“…An important feature of EDDB(r) is that it allows evaluating both local (EDDB P (r)) and global (EDDB G (r)) aromaticity. A mathematical definition of EDDB and the theory behind it can be found in papers by Szczepanik [99][100][101][102]. From a practical point of view, it is worth mentioning that the RunEDDB program, written by Szczepanik and available online [118], allows the calculation of values of various EDDB variants, further dissection of the π and σ electron contributions to each variant, and the visualization of the π-electron circuits.…”

Section: Electron Delocalization Indicesmentioning

confidence: 99%

Aromaticity Concepts Derived from Experiments

Szatyłowicz

Wieczorkiewicz

Krygowski

2022

Sci

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“…The chapter on arenes by Roberts and Caserio begins as follows: “The so-called aromatic hydrocarbons, or arenes, are cyclic unsaturated compounds that have such strikingly different chemical properties from conjugated alkenes (polyenes) that it is convenient to consider them as a separate class of hydrocarbon.” 1 It is thus clear that even if aromaticity is argued to be suspicious 2 or ill-defined, 3 this concept is in the center of organic chemistry 4 and allows rationalization of the behavior of “cyclic unsaturated compounds.” Aromaticity requires an enumerative 4 , 5 rather than a strict and simple definition which addresses the (1) energetic, 6 (2) geometric, 7 (3) magnetic, 8 (4) electronic (electron density), 9 (5) chemical reactivity, 6 (6) graph theory, 10 , 11 and other 4 criteria. Each of the aromaticity conditions has been used to formulate the aromaticity index, allowing for a quantitative evaluation of this very aromaticity aspect.…”

Section: Introductionmentioning

confidence: 99%

“…1 It is thus clear that even if aromaticity is argued to be suspicious 2 or ill-defined, 3 this concept is in the center of organic chemistry 4 and allows rationalization of the behavior of "cyclic unsaturated compounds." Aromaticity requires an enumerative 4,5 rather than a strict and simple definition which addresses the (1) energetic, 6 (2) geometric, 7 (3) magnetic, 8 (4) electronic (electron density), 9 (5) chemical reactivity, 6 (6) graph theory, 10,11 and other 4 criteria. Each of the aromaticity conditions has been used to formulate the aromaticity index, allowing for a quantitative evaluation of this very aromaticity aspect.…”

Section: Introductionmentioning

confidence: 99%

On Aromaticity of the Aromatic α-Amino Acids and Tuning of the NICS Indices to Find the Aromaticity Order

2022

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The NICS aromaticity indices of the rings in flexible phenylalanine (Phe), tryptophan (Trp), tyrosine (Tyr), and histidine (His) chiral molecules were analyzed. These molecules have several dozens of conformers, and their rings are slightly non-planar. Therefore, the population-averaged NICS pav index was defined, and the NICS scans had to be performed with respect to planes found by the least-squares routine. A rule differentiating an obverse and a reverse ring face in aromatic amino acids was formulated. The NICS scan minima corresponding to the obverse and reverse face were unequal, which prompted us to use the term ring face aromaticity/ring face tropicity. It appeared that for Phe, Trp, Tyr, and His, the reverse face has always had higher ring face aromaticity/ring face tropicity than the obverse one. Despite the NICS modifications, uncertainty about the amino acid aromaticity order remained. This motivated us to use the integral INICS index newly proposed by Stanger as well. Then, the following sequence was obtained: Trp(phenyl) > Phe > Trp(pyrrole) > His > Tyr. The juxtaposition of the INICS indices of amino acids with that of some model rings revealed a fair transferability of the values. Finally, analysis of the substituent effect on INICS demonstrated that the aromaticity of Tyr is the lowest due to the strength of the OH group π-electron-donating effect able to perturb enough the ring charge distribution and its magnetic aromaticity. The NICS calculations were executed using the ARONICS program written within the project.

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The electron density of delocalized bonds (EDDBs) as a measure of local and global aromaticity

Cited by 21 publications

References 56 publications

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C₁₈) Precursors, C₁₈‐(CO)_n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (‐CO) Groups**

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C₁₈) Precursors, C₁₈‐(CO)_n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (‐CO) Groups**

Aromaticity Concepts Derived from Experiments

On Aromaticity of the Aromatic α-Amino Acids and Tuning of the NICS Indices to Find the Aromaticity Order

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The electron density of delocalized bonds (EDDBs) as a measure of local and global aromaticity

Cited by 21 publications

References 56 publications

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C18) Precursors, C18‐(CO)n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (‐CO) Groups**

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C18) Precursors, C18‐(CO)n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (‐CO) Groups**

Aromaticity Concepts Derived from Experiments

On Aromaticity of the Aromatic α-Amino Acids and Tuning of the NICS Indices to Find the Aromaticity Order

Contact Info

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Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C₁₈) Precursors, C₁₈‐(CO)_n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (‐CO) Groups**

Bonding Character, Electron Delocalization, and Aromaticity of Cyclo[18]Carbon (C₁₈) Precursors, C₁₈‐(CO)_n (n=6, 4, and 2): Focusing on the Effect of Carbonyl (‐CO) Groups**