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Ke An - One of the best experts on this subject based on the ideXlab platform.
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evaluation of triplet Aromaticity by the indene isoindene isomerization stabilization energy method
European Journal of Organic Chemistry, 2014Co-Authors: Ke AnAbstract:Aromaticity, one of the most important concepts in chemistry, has attracted considerable interest from both experimentalists and theoreticians. According to Baird's rule, triplet annulenes with 4n π electrons are aromatic. However, the approach to evaluate the magnitude of the triplet Aromaticity is less developed. Herein we apply the indene–isoindene isomerization stabilization energy (ISE) method to evaluate the Aromaticity in the triplet state. The reliability of this approach can be demonstrated by the strong correlation of these indene–isoindene ISE values with nucleus-independent chemical shifts [NICS(1)zz] as well as methyl–methylene ISE values. Large [4n]annulenes have the tendency to be planar to achieve Aromaticity in the T1 state. Steric effects play an important role in the stabilities of large [4n]annulene isomers.
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Evaluation of Triplet Aromaticity by the Indene–Isoindene Isomerization Stabilization Energy Method
European Journal of Organic Chemistry, 2014Co-Authors: Ke AnAbstract:Aromaticity, one of the most important concepts in chemistry, has attracted considerable interest from both experimentalists and theoreticians. According to Baird's rule, triplet annulenes with 4n π electrons are aromatic. However, the approach to evaluate the magnitude of the triplet Aromaticity is less developed. Herein we apply the indene–isoindene isomerization stabilization energy (ISE) method to evaluate the Aromaticity in the triplet state. The reliability of this approach can be demonstrated by the strong correlation of these indene–isoindene ISE values with nucleus-independent chemical shifts [NICS(1)zz] as well as methyl–methylene ISE values. Large [4n]annulenes have the tendency to be planar to achieve Aromaticity in the T1 state. Steric effects play an important role in the stabilities of large [4n]annulene isomers.
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evaluation of triplet Aromaticity by the isomerization stabilization energy
Organic Letters, 2013Co-Authors: Ke An, Paul Von Rague SchleyerAbstract:The many manifestations of Aromaticity have long fascinated both experimentalists and theoreticians. Due to their degenerate half-filled MOs, triplet [n]annulenes with 4n π-electrons are also aromatic, but the degree of their stabilization has been difficult to quantify. The isomerization stabilization energy (ISE) method has been applied to evaluate the triplet Aromaticity. The reliability of this approach is indicated by the strong correlation of the ISE results with NICS(1)zz, a magnetic indicator of triplet state Aromaticity.
Miquel Solà - One of the best experts on this subject based on the ideXlab platform.
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Electron Delocalization in Planar Metallacycles: Hückel or Möbius Aromatic?
ChemistryOpen, 2019Co-Authors: Dariusz W. Szczepanik, Miquel SolàAbstract:In this work the relationship between the formal number of π-electrons, d-orbital conjugation topology, π-electron delocalization and Aromaticity in d-block metallacycles is investigated in the context of recent findings concerning the correlation of π-HOMO topology and the magnetic Aromaticity indices in these species. It is demonstrated that for π-electron rich d-metallacycles the direct link between Aromaticity, the number of π-electrons and the frontier π-orbital topology does not strictly hold and for such systems it is very difficult to unambiguously associate their Aromaticity with the "4n+2" (Huckel) and "4n" (Mobius) rules. It is also shown that the recently proposed electron density of delocalized bonds (EDDB) method can successfully be used not only to quantify and visualize Aromaticity in such difficult cases, but also - in contrast to magnetic Aromaticity descriptors - to provide a great deal of information on the real role of d-orbitals in metallacycles without the ambiguity of bookkeeping of electrons in the π-subsystem of the molecular ring. Interestingly, some of the metallacycles studied cannot be classified exclusively as Huckel or Mobius because they have a hybrid Huckel-Mobius or even quasi-aromatic nature.
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Rules of Aromaticity
Challenges and Advances in Computational Chemistry and Physics, 2016Co-Authors: Ferran Feixas, Jordi Poater, Eduard Matito, Miquel SolàAbstract:The concept of Aromaticity is elusive; it is not directly observable. Somewhat surprisingly, given the fuzzy character of this concept, there exist a number of very simple mathematical rules that can account for the Aromaticity of a large number of organic and inorganic molecules. Among them we can mention Huckel’s, Baird’s, Wade-Mingos’, and Hirsch’s rules. In this chapter we summarize recent advances carried out in our group in the study of these Aromaticity rules.
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quantifying Aromaticity with electron delocalisation measures
Chemical Society Reviews, 2015Co-Authors: Ferran Feixas, Jordi Poater, Eduard Matito, Miquel SolàAbstract:Aromaticity cannot be measured directly by any physical or chemical experiment because it is not a well-defined magnitude. Its quantification is done indirectly from the measure of different properties that are usually found in aromatic compounds such as bond length equalisation, energetic stabilisation, and particular magnetic behaviour associated with induced ring currents. These properties have been used to set up the myriad of structural-, energetic-, and magnetic-based indices of Aromaticity known to date. The cyclic delocalisation of mobile electrons in two or three dimensions is probably one of the key aspects that characterise aromatic compounds. However, it has not been until the last decade that electron delocalisation measures have been widely employed to quantify Aromaticity. Some of these new indicators of Aromaticity such as the PDI, FLU, ING, and INB were defined in our group. In this paper, we review the different existing descriptors of Aromaticity that are based on electron delocalisation properties, we compare their performance with indices based on other properties, and we summarise a number of applications of electronic-based indices for the analysis of Aromaticity in interesting chemical problems.
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Electron delocalization and Aromaticity in low-lying excited states of archetypal organic compounds
Physical chemistry chemical physics : PCCP, 2011Co-Authors: Ferran Feixas, Patrick Bultinck, Jelle Vandenbussche, Eduard Matito, Miquel SolàAbstract:Aromaticity is a property usually linked to the ground state of stable molecules. Although it is well-known that certain excited states are unquestionably aromatic, the Aromaticity of excited states remains rather unexplored. To move one step forward in the comprehension of Aromaticity in excited states, in this work we analyze the electron delocalization and Aromaticity of a series of low-lying excited states of cyclobutadiene, benzene, and cyclooctatetraene with different multiplicities at the CASSCF level by means of electron delocalization measures. While our results are in agreement with Baird's rule for the Aromaticity of the lowest-lying triplet excited state in annulenes having 4nπ-electrons, they do not support Soncini and Fowler's generalization of Baird's rule pointing out that the lowest-lying quintet state of benzene and septet state of cyclooctatetraene are not aromatic.
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Theoretical studies on Aromaticity of selected hydroxypyrones. Part 3. ChelatoAromaticity phenomenon in metalcomplexes of hydroxypyrones.
Journal of Physical Organic Chemistry, 2010Co-Authors: Krzysztof Zborowski, Jordi Poater, Miquel Solà, Leonard ProniewiczAbstract:The aim of this project is to study the aromatic properties of various forms (neutral, cationic and anionic) of selected hydroxypyrones (pyromeconic acid, maltol, ethylmaltol) and their metal complexes with aluminium, gallium, and indium ions. Aromaticity of hydroxypyrone metalcomplexes is important because it can influence the stability of such complexes, which is crucial for their applications in medicinal and environmental chemistry. Results from ten different indices of Aromaticity (HOMA, NICS(0), NICS(1) NICSscan, ASEiso, PDI, FLU, Iring, MCI, and KMCI) show that Aromaticity in hydroxypyrones decreases in the order cations > neutral molecules > anions. Performed calculations situate the aromaticities of ligands in metal complexes close to their respective cations. This means that complexation causes a significant increase of the Aromaticity of ligands, which stabilizes formed chelatocomplexes. On the other hand, we clearly show that rings that are involved in binding metal ions are not aromatic.
Alexander I. Boldyrev - One of the best experts on this subject based on the ideXlab platform.
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Usefulness of the σ‐Aromaticity and σ‐AntiAromaticity Concepts for Clusters and Solid‐State Compounds
Chemistry (Weinheim an der Bergstrasse Germany), 2017Co-Authors: Ivan A. Popov, Alyona A. Starikova, D. V. Steglenko, Alexander I. BoldyrevAbstract:In this Review we present examples of clusters, molecules, and solid-state compounds, for which the use of σ-Aromaticity and σ-antiAromaticity concepts is essential for understanding of chemical bonding. We show that the bonding patterns in these σ-aromatic and σ-antiaromatic compounds are similar to those of the corresponding π-aromatic and π-antiaromatic chemical systems, respectively. Undoubtedly, σ-Aromaticity helps us understand why the high symmetry isomers are the most stable among myriads of other potential structures. We also show that besides systems exhibiting either σ- or π-aromatic features, there are species, which can possess multiple Aromaticity/antiAromaticity, or conflicting Aromaticity patterns. We believe that the σ-Aromaticity and σ-antiAromaticity concepts will be helpful in rationalizing chemical bonding, structure, stability, and molecular properties of chemical species in both organic and inorganic chemistry. We hope that they will also be useful for other areas of science such as material science, catalysis, nanotechnology, and biochemistry.
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beyond organic chemistry Aromaticity in atomic clusters
ChemInform, 2016Co-Authors: Alexander I. Boldyrev, Lai-sheng WangAbstract:We describe joint experimental and theoretical studies carried out collaboratively in the authors' labs for understanding the structures and chemical bonding of novel atomic clusters, which exhibit Aromaticity. The concept of Aromaticity was first discovered to be useful in understanding the square-planar unit of Al4 in a series of MAl4− bimetallic clusters that led to discoveries of Aromaticity in many metal cluster systems, including transition metals and similar cluster motifs in solid compounds. The concept of Aromaticity has been found to be particularly powerful in understanding the stability and bonding in planar boron clusters, many of which have been shown to be analogous to polycyclic aromatic hydrocarbons in their π bonding. Stimulated by the multiple Aromaticity in planar boron clusters, a design principle has been proposed for stable metal-cerntered aromatic molecular wheels of the general formula, M@Bnk−. A series of such borometallic aromatic wheel complexes have been produced in supersonic cluster beams and characterized experimentally and theoretically, including Ta@B10− and Nb@B10−, which exhibit the highest coordination number in two dimensions.
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Deciphering Aromaticity in porphyrinoids via adaptive natural density partitioning
Organic & biomolecular chemistry, 2014Co-Authors: Alexander S. Ivanov, Alexander I. BoldyrevAbstract:The adaptive natural density partitioning (AdNDP) method has been applied for the first time to porphyrinoids in order to describe their Aromaticity. The analysis of π-electron system reveals that Aromaticity of annulene originates from 6-π-electron delocalization, while Aromaticity of porphyrin can be better described in terms of local aromaticities of the appended 6-π-electron pyrrolic heterocycles and 6-π-electron central fragment. The patterns of chemical bonding for porphyrinoids obtained by AdNDP are consistent with chemical intuition and lead to unique and compact graphic formulas.
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Aromaticity and AntiAromaticity in Inorganic Chemistry
Comprehensive Inorganic Chemistry II, 2013Co-Authors: Timur R. Galeev, Alexander I. BoldyrevAbstract:The concept of Aromaticity, initially introduced for organic compounds, has significantly expanded to include inorganic species and proved to be a useful tool to rationalize their structures, bonding, and properties. Inorganic rings often exhibit Aromaticity, antiAromaticity, or conflicting Aromaticity of a more complex nature compared to Aromaticity/antiAromaticity of prototypical organic molecules. In this chapter, we review theoretically predicted and/or experimentally isolated main group and transition metal compounds which exhibit Aromaticity, antiAromaticity, or conflicting Aromaticity.
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Multiple Aromaticity, Multiple AntiAromaticity, and Conflicting Aromaticity in Planar Clusters
Nanoclusters - A Bridge across Disciplines, 2010Co-Authors: Dmitry Yu. Zubarev, Alexander I. BoldyrevAbstract:Abstract The possible types of σ-, π-, and δ-Aromaticity, antiAromaticity, and conflicting Aromaticity in small- and medium-sized planar clusters are discussed. We show that the electron counting rule for Aromaticity/antiAromaticity (singlet coupling case) should be applied separately for each of delocalized σ-, π-, and δ-system present in the cluster. If the aromatic subsystem includes radial and tangential parts, for example, σ-Aromaticity/antiAromaticity based on p-atomic orbitals (AOs) and π-Aromaticity/antiAromaticity based on d-AOs, the counting rules for cyclic structures with even number of vertices are 4 n + 4(Aromaticity)/4 n + 6(antiAromaticity) and for cyclic structures with odd number of vertices they are 4 n + 2(Aromaticity)/4 n (antiAromaticity). We also demonstrate that in boron, carbon, and borocarbon clusters the chemical bonding model should necessarily include the presence of 2c–2e B–B, C–C, and B–C peripheral bonds, respectively, in addition to the delocalized bonding. The delocalized bonding can be classified as multiple aromatic, multiple antiaromatic, and conflicting aromatic. The globally antiaromatic systems could also be treated as systems with island Aromaticity. We believe that the peripheral 2c–2e C–C, B–C, and B–B bonds are responsible for the stability and planarity or quasi-planarity of medium carbon, boron, and borocarbon clusters. When lone pairs are encountered instead of 2c–2e peripheral bonds, the deviation from planarity occurs in favor of three-dimensional structures. Aluminum and silicon clusters illustrate this point of view, because they become three-dimensional as their size increases beyond five and four atoms, respectively. At this moment, we believe that the chemical bonding model for the planar clusters is well developed and can be used to explain the structure, stability, reactivity, and other cluster properties.
Shubin Liu - One of the best experts on this subject based on the ideXlab platform.
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Global and local Aromaticity of acenes from the information-theoretic approach in density functional reactivity theory.
Physical Chemistry Chemical Physics, 2019Co-Authors: Thijs Stuyver, Chunying Rong, Mercedes Alonso, Frank De Proft, Paul Geerlings, Shubin LiuAbstract:In this work, we report a systematic study on the global and local Aromaticity of acenes using a series of model structures from 2-acene to 11-acene. A recently developed ansatz, an information-theoretic approach coached into density functional reactivity theory has been employed, which essentially provides different density functionals characterizing the molecular electron density distribution. Based on the correlation analysis of six conventional Aromaticity indices with eight information-theoretic quantities, we examined the Aromaticity of acenes from both global and local perspectives. From the global Aromaticity viewpoint, our results suggest that different descriptors based on various physicochemical properties are intrinsically dependent. A novel laminated feature ruling local Aromaticity of acenes has been unveiled, from which we found that the distance from the terminal rings plays the critical role. Based on the shape of the correlation plots between the conventional Aromaticity indices and information-theoretic quantities, the latter could be separated into three subgroups. The seemingly contradictory results from global and local Aromaticity perspectives not only present us the uniqueness of the acene systems but all demonstrate the effectiveness of the information-theoretic approach from density functional reactivity theory. Besides strengthening the validity of a series of new Aromaticity descriptors, our results should lead to more clear insights into the chemical significance of the information-theoretic quantities.
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Aromaticity and antiAromaticity of substituted fulvene derivatives perspectives from the information theoretic approach in density functional reactivity theory
Physical Chemistry Chemical Physics, 2017Co-Authors: Chunying Rong, Pratim K. Chattaraj, Frank De Proft, Shubin LiuAbstract:Even though the concept of Aromaticity and antiAromaticity is extremely important and widely used, there still exist lots of controversies in the literature, which are believed to be originated from the fact that there are so many aromatic types discovered and at the same time there are many Aromaticity indexes proposed. In this work, using seven series of substituted fulvene derivatives as an example and with the information-theoretic approach in density functional reactivity theory, we examine these concepts from a different perspective. We investigate the changing patterns of Shannon entropy, Fisher information, Ghosh–Berkowitz–Parr entropy, information gain, Onicescu information energy, and relative Renyi entropy on the ring carbon atoms of these systems. Meanwhile, we also consider variation trends of four representative kinds of Aromaticity indexes such as FLU, HOMA, ASE and NICS. Statistical analyses among these quantities show that with the same ring structure of the derivatives, both information-theoretic quantities and Aromaticity indexes obey the same changing pattern, which are valid across all seven systems studied. However, cross correlations between these two sets of quantities yield two completely opposite patterns. These ring-structure dependent correlations are in good agreement with Huckel's 4n + 2 rule of Aromaticity and 4n rule of antiAromaticity. Our results should provide a novel and complementary viewpoint on how Aromaticity and antiAromaticity should be appreciated and categorized. More studies are in progress to further our understanding about the matter.
Jun Zhu - One of the best experts on this subject based on the ideXlab platform.
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Adaptive Aromaticity in ruthenacycles
Theoretical Chemistry Accounts, 2020Co-Authors: Dandan Chen, Rulin Qiu, Shicheng Dong, Jun ZhuAbstract:Adaptive Aromaticity in the lowest singlet and triplet states is a rare property found among molecular systems. So far, only osmapentalene and osmapyridinium have been found to possess the adaptive Aromaticity. Although it has been confirmed that the pattern of electron excitation is a key factor to achieve the adaptive Aromaticity, further investigation of the metal center effect has not yet been made. Ruthenium, another Group 8 transition metal, can form metallacycles similar to the osmium counterparts. Here, we perform density functional theory calculations for two sets of ruthenacycles and analyze their Aromaticity with multiple indices, revealing a 16-valence-electron ruthenapentalene being aromatic in both the singlet ground state (S0) and the lowest triplet state (T1) and extending the adaptive Aromaticity to the second-row transition metal complexes.
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Dual Aromaticity in Both the T0 and S1 States: Osmapyridinium with Phosphonium Substituents
2019Co-Authors: Ting Shen, Dandan Chen, Lu Lin, Jun ZhuAbstract:According to Hückel’s and Baird’s rules, cyclic conjugated species are aromatic either in the ground state or in the excited state only. Thus, species with Aromaticity in both states (denoted as adaptive Aromaticity) are particularly rare. Here we carry out density functional theory calculations on a series of osmapyridine and osmapyridinium complexes (96 species) and find that 2 of them display adaptive Aromaticity, which was verified by various Aromaticity indices including HOMA, ELFπ, MCI, ACIDπ plots, and the heat of hydrogenation. Further study reveals that two osmapyridiniums containing one or two phosphonium substituents exhibit the character of the triplet ground state, which was supported by the high-level coupled cluster calculations. Our findings highlight the importance of a transition metal and phosphoniums in achieving adaptive Aromaticity and the triplet ground state and may aid the design of organometallics for photochemical and molecular magnetism applications
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Probing the Strongest Aromatic Cyclopentadiene Ring by Hyperconjugation
Organometallics, 2018Co-Authors: Qiong Xie, Tingting Sun, Jun ZhuAbstract:Hyperconjugation, an interaction of electrons in a σ orbital or lone pair with an adjacent π or even σ antibonding orbital, can have a strong effect on Aromaticity. However, most work on hyperconjugative Aromaticity has been limited to main-group substituents. Here, we report a thorough density functional theory study to evaluate the Aromaticity in various cyclopentadienes that contain both main-group and transition-metal substituents. Our calculations reveal that the strongest aromatic cyclopentadiene ring can be achieved by the synergy of trans influence and hyperconjugation caused by transition-metal substituents. Our findings highlight the great power of transition metals and trans influence in achieving hyperconjugative Aromaticity, opening an avenue to the design of other novel aromatic organometallics.
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Probing the Strongest Aromatic Cyclopentadiene Ring by Hyperconjugation
2018Co-Authors: Qiong Xie, Tingting Sun, Jun ZhuAbstract:Hyperconjugation, an interaction of electrons in a σ orbital or lone pair with an adjacent π or even σ antibonding orbital, can have a strong effect on Aromaticity. However, most work on hyperconjugative Aromaticity has been limited to main-group substituents. Here, we report a thorough density functional theory study to evaluate the Aromaticity in various cyclopentadienes that contain both main-group and transition-metal substituents. Our calculations reveal that the strongest aromatic cyclopentadiene ring can be achieved by the synergy of trans influence and hyperconjugation caused by transition-metal substituents. Our findings highlight the great power of transition metals and trans influence in achieving hyperconjugative Aromaticity, opening an avenue to the design of other novel aromatic organometallics
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triplet state Aromaticity nics criterion hyperconjugation and charge effects
Chemistry-an Asian Journal, 2016Co-Authors: Hongchao Sun, Jun ZhuAbstract:Aromaticity, one of the most important concepts in organic chemistry, has attracted considerable interest from both experimentalists and theoreticians. It remains unclear which NICS index is best to evaluate the triplet-state Aromaticity. Here, we carry out thorough density functional theory (DFT) calculations to examine this issue. Our results indicate that among the various computationally available NICS indices, NICS(1)zz is the best for the triplet state. The correlations can be improved from 0.840 to 0.938 when only neutral species are considered, demonstrating the significant effect of the charge on the triplet-state Aromaticity. In addition, calculations suggest that five-membered cyclic species with "hyperconjugative" Aromaticity (and antiAromaticity) in the S0 state will become antiaromatic (and aromatic) in the T1 state, indicating an important role of hyperconjugation. Finally, a moderate correlation (r(2) =0.708) is identified between the NICS(1)zz values and spin distributions.