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Riera Aroche R, Ortiz García YM, Martínez Arellano MA, Riera Leal A. DNA as a perfect quantum computer based on the quantum physics principles. Sci Rep 2024; 14:11636. [PMID: 38773193 PMCID: PMC11109248 DOI: 10.1038/s41598-024-62539-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2024] [Accepted: 05/17/2024] [Indexed: 05/23/2024] Open
Abstract
DNA is a complex multi-resolution molecule whose theoretical study is a challenge. Its intrinsic multiscale nature requires chemistry and quantum physics to understand the structure and quantum informatics to explain its operation as a perfect quantum computer. Here, we present theoretical results of DNA that allow a better description of its structure and the operation process in the transmission, coding, and decoding of genetic information. Aromaticity is explained by the oscillatory resonant quantum state of correlated electron and hole pairs due to the quantized molecular vibrational energy acting as an attractive force. The correlated pairs form a supercurrent in the nitrogenous bases in a single band π -molecular orbital ( π -MO). The MO wave function ( Φ ) is assumed to be the linear combination of the n constituent atomic orbitals. The central Hydrogen bond between Adenine (A) and Thymine (T) or Guanine (G) and Cytosine (C) functions like an ideal Josephson Junction. The approach of a Josephson Effect between two superconductors is correctly described, as well as the condensation of the nitrogenous bases to obtain the two entangled quantum states that form the qubit. Combining the quantum state of the composite system with the classical information, RNA polymerase teleports one of the four Bell states. DNA is a perfect quantum computer.
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Affiliation(s)
- R Riera Aroche
- Department of Research in Physics, University of Sonora, Hermosillo, Sonora, Mexico
- Research and Higher Education Center of UNEPROP, Hermosillo, Sonora, Mexico
| | - Y M Ortiz García
- Research Institute of Dentistry, University of Guadalajara, Guadalajara Jalisco, Mexico
- Research and Higher Education Center of UNEPROP, Hermosillo, Sonora, Mexico
| | - M A Martínez Arellano
- General Hospital of the State of Sonora, Boulevar José María Escrivá de Balaguer 157, Colonia Villa del Palmar, C.P. 83105, Hermosillo, Sonora, Mexico
- Research and Higher Education Center of UNEPROP, Hermosillo, Sonora, Mexico
| | - A Riera Leal
- General Hospital of the State of Sonora, Boulevar José María Escrivá de Balaguer 157, Colonia Villa del Palmar, C.P. 83105, Hermosillo, Sonora, Mexico.
- Research and Higher Education Center of UNEPROP, Hermosillo, Sonora, Mexico.
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Ismael AK, Al-Jobory A. Energy gap and aromatic molecular rings. ROYAL SOCIETY OPEN SCIENCE 2024; 11:231533. [PMID: 38577212 PMCID: PMC10987978 DOI: 10.1098/rsos.231533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 02/04/2024] [Accepted: 02/13/2024] [Indexed: 04/06/2024]
Abstract
The manuscript combines rational density functional theory simulations and experimental data to investigate the electrical properties of eight polycyclic aromatic hydrocarbons (PAHs). The optimized geometries reveal a preference for one-row, two-row and three-row ring distributions. Band structure plots demonstrate an inverse correlation between the number of aromatic rings and band gap size, with a specific order observed across the PAHs. Gas phase simulations support these findings, though differences in values are noted compared to the literature. Introducing a two-row ring distribution concept resolves discrepancies, particularly in azulene. The B3LYP function successfully bridges theoretical and experimental gaps, particularly in large PAHs. The manuscript highlights the potential for designing electronic devices based on different-sized PAHs, emphasizing a multi-ring distribution approach and opening new avenues for practical applications.
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Affiliation(s)
- Ali K. Ismael
- Department of Physics, Lancaster University, LancasterLA1 4YB, UK
- Department of Physics, College of Education for Pure Science, Tikrit University, Tikrit, Salah Al Deen34001, Iraq
| | - Alaa Al-Jobory
- Department of Physics, Lancaster University, LancasterLA1 4YB, UK
- Department of Physics, College of Science, University of Anbar, Al Rumadi, Al Anbar31001, Iraq
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Okazawa K, Tsuji Y, Yoshizawa K. Frontier Orbital Views of Stacked Aromaticity. J Phys Chem A 2023. [PMID: 37243683 DOI: 10.1021/acs.jpca.3c00360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
Recent studies have theoretically and experimentally demonstrated that antiaromatic molecules with 4n π electrons exhibit stacked aromaticity according to π-π stacking when arranged in a face-to-face manner. However, the mechanism of its occurrence has not been clearly studied. In this study, we investigated the mechanism of stacked aromaticity using cyclobutadiene. When the antiaromatic molecules are stacked in a face-to-face manner, the orbital interactions between the degenerate singly occupied molecular orbitals (SOMOs) of the monomer unit cause a larger energy gap between the degenerate highest-occupied molecular orbitals (HOMOs) and the lowest-unoccupied molecular orbitals (LUMOs) of the dimer. However, the antiaromatic molecules are more stable in less symmetric conformations, mainly because of pseudo-Jahn-Teller distortions. In the case of cyclobutadiene, the two SOMOs of the monomer unit split into HOMO and LUMO because of the bond alternation. When the molecules are stacked in a face-to-face manner, the HOMO-LUMO gap of the dimer is smaller than that of the monomer due to the interactions between the HOMOs and LUMOs of the two monomer units. When the monomer units are within a specific distance of each other, the HOMO and LUMO of the dimer, which correspond to antibonding and bonding between the units, respectively, are interchanged. This alternation of molecular orbitals may result in an increase in the bond strength between the monomer units, exhibiting stacked aromaticity. We demonstrated that it is possible to control the distance exhibited by stacked aromaticity by engineering the HOMO-LUMO gap of the monomer units.
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Affiliation(s)
- Kazuki Okazawa
- Institute for Materials Chemistry and Engineering and IRCCS, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
| | - Yuta Tsuji
- Faculty of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
| | - Kazunari Yoshizawa
- Institute for Materials Chemistry and Engineering and IRCCS, Kyushu University, Nishi-ku, Fukuoka 819-0395, Japan
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4
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Shaik S, Danovich D, Hiberty PC. On The Nature of the Chemical Bond in Valence Bond Theory. J Chem Phys 2022; 157:090901. [DOI: 10.1063/5.0095953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
This perspective outlines a panoramic description of the nature of the chemical bond according to valence bond theory. It describes single bonds, and charge-shift bonds (CSBs) in which the entire/most of the bond energy arises from the resonance between the covalent and ionic structures of the bond. Many CSBs are homonuclear bonds. Hypervalent molecules are CSBs. Then we describe multiply bonded molecules with emphasis on C2 and 3O2. The perspective outlines an effective methodology of peeling the electronic structure to the necessary minimum: a structure with a quadruple bond, and two minor structures with double bonds, which stabilize the quadruple bond by resonance. 3O2 is chosen because it is a persistent diradical. The persistence of 3O2 is due to the large CSB resonance interaction of the π-3-electron bonds. Subsequently, we describe the roles of π vs. σ in the geometric preferences in unsaturated molecules, and their Si-based analogs. Then, the perspective discusses bonding in clusters of univalent metal-atoms, which possess only parallel spins, and are nevertheless bonded due to multiple resonance interactions. The bond energy reaches ~40 kcal/mol for a pair of atoms (in n+1Cun; n~10-12). The final subsection discusses singlet excited states in ethene, ozone and SO2. It demonstrates the capability of the breathing-orbital VB method to yield an accurate description of a variety of excited states using 10 or less VB structures. Furthermore, the method underscores covalent structures which play a key role in the correct description and bonding of these excited states.
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Affiliation(s)
- Sason Shaik
- Hebrew University of Jerusalem Institute of Chemistry, Israel
| | - David Danovich
- Hebrew University of Jerusalem Institute of Chemistry, Israel
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Seeman JI. History of the Woodward-Hoffmann Rules. The No-Mechanism Puzzle. CHEM REC 2022; 22:e202100212. [PMID: 35174963 DOI: 10.1002/tcr.202100212] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Revised: 11/13/2021] [Indexed: 11/11/2022]
Abstract
This is Paper 2 in the 27-paper series on the history of the development of the Woodward-Hoffmann rules. Paper 2 takes the reader back to the 1950s and early 1960s, before the publication of the first Woodward-Hoffmann paper in January 1965. The scope of the pericyclic no-mechanism problem is described along with many of the key "hints" or "clues" to orbital symmetry control that were available in the literature prior to 1965. A chronology of reactions with alternating stereospecificities is provided. A second chronology of alternating theoretical hints is provided, e. g., 4n+2 versus 4n. Another chronology is provided, that of the development of frontier molecular orbital theory, with and without phases and nodes. A tabulation is provided of 36 instances in which the MOs of 1,3-butadiene were reported in the literature. A knowledge of the MOs of 1,3-butadiene, plus a knowledge of some of the alternating stereospecific reactions, could have led many chemists to the solution of the pericyclic no-mechanism problem before Woodward and Hoffmann.
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Affiliation(s)
- Jeffrey I Seeman
- Department of Chemistry, University of Richmond, 23173, Richmond, VA, USA
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Reuter L, Lüchow A. Real space electron delocalization, resonance, and aromaticity in chemistry. Nat Commun 2021; 12:4820. [PMID: 34376667 PMCID: PMC8355119 DOI: 10.1038/s41467-021-25091-8] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Accepted: 07/19/2021] [Indexed: 11/10/2022] Open
Abstract
Chemists explaining a molecule’s stability and reactivity often refer to the concepts of delocalization, resonance, and aromaticity. Resonance is commonly discussed within valence bond theory as the stabilizing effect of mixing different Lewis structures. Yet, most computational chemists work with delocalized molecular orbitals, which are also usually employed to explain the concept of aromaticity, a ring delocalization in cyclic planar systems which abide certain number rules. However, all three concepts lack a real space definition, that is not reliant on orbitals or specific wave function expansions. Here, we outline a redefinition from first principles: delocalization means that likely electron arrangements are connected via paths of high probability density in the many-electron real space. In this picture, resonance is the consideration of additional electron arrangements, which offer alternative paths. Most notably, the famous 4n + 2 Hückel rule is generalized and derived from nothing but the antisymmetry of fermionic wave functions. The concept of delocalization, resonance and aromaticity are commonly discussed within electronic structure frameworks relying on specific wave function expansions. Here the authors propose a redefinition of these concepts from first-principles by investigating saddle points of the all-electron probability density.
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Affiliation(s)
- Leonard Reuter
- Institute of Physical Chemistry, RWTH Aachen University, Aachen, Germany
| | - Arne Lüchow
- Institute of Physical Chemistry, RWTH Aachen University, Aachen, Germany.
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Shaik S, Danovich D, Hiberty PC. Valence Bond Theory-Its Birth, Struggles with Molecular Orbital Theory, Its Present State and Future Prospects. Molecules 2021; 26:molecules26061624. [PMID: 33804038 PMCID: PMC8001733 DOI: 10.3390/molecules26061624] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Revised: 03/08/2021] [Accepted: 03/10/2021] [Indexed: 01/04/2023] Open
Abstract
This essay describes the successive births of valence bond (VB) theory during 1916–1931. The alternative molecular orbital (MO) theory was born in the late 1920s. The presence of two seemingly different descriptions of molecules by the two theories led to struggles between the main proponents, Linus Pauling and Robert Mulliken, and their supporters. Until the 1950s, VB theory was dominant, and then it was eclipsed by MO theory. The struggles will be discussed, as well as the new dawn of VB theory, and its future.
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Affiliation(s)
- Sason Shaik
- Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel;
- Correspondence: (S.S.); (P.C.H.)
| | - David Danovich
- Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel;
| | - Philippe C. Hiberty
- CNRS, Institut de Chimie Physique UMR8000, Université Paris-Saclay, 91405 Orsay, France
- Correspondence: (S.S.); (P.C.H.)
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8
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Shaik S. Stories of My Journeys Through Valence Bond Theory, DFT, MD and their Applications to Complex Objects. Isr J Chem 2020. [DOI: 10.1002/ijch.202000090] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Sason Shaik
- Institute of Chemistry The Hebrew University of Jerusalem Edmond J. Safra Campus, Givat Ram 91904 Jerusalem Israel
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Kudo T, Schmidt MW, Matsunaga N. Ab Initio Molecular Orbital Study of the First Four Si/C Alternately Substituted Annulenes. J Phys Chem A 2019; 123:4588-4598. [DOI: 10.1021/acs.jpca.9b02631] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Takako Kudo
- Division of Pure and Applied Science, Graduate School of Science and Technology, Gunma University, Kiryu 376-8515, Japan
| | - Michael W. Schmidt
- Department of Chemistry, Iowa State University, Ames, Iowa 50011-2030, United States
| | - Nikita Matsunaga
- Department of Chemistry & Biochemistry, Long Island University, Brooklyn, New York 11201, United States
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11
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Latorre S, Moreira IDPR, Villacampa B, Julià L, Velasco D, Bofill JM, López-Calahorra F. Differential Behavior of Amino-Imino Constitutional Isomers in Nonlinear Optical Processes. Chemphyschem 2010; 11:912-9. [DOI: 10.1002/cphc.200900616] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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12
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Malrieu JP, Gicquel M, Fowler PW, Lepetit C, Heully JL, Chauvin R. Direct evaluation of cyclic contributions to the pi energy of conjugated hydrocarbons from strongly localized zero-order pictures. J Phys Chem A 2008; 112:13203-14. [PMID: 18817362 DOI: 10.1021/jp802839n] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This paper presents a new procedure for identifying that part of the pi electronic energy of conjugated hydrocarbons which results from cyclic circulation of electrons around a ring. It first shows that one may calculate perturbatively the ground state energy of the Hückel Hamiltonian from a strongly localized Kekulé-type zero-order wave function. The contributions due to cyclic circulation of the electrons appear explicitly, in terms of the interatomic hopping integral t, at the second order in cyclobutadiene (where it is equal to -t (antiaromatic)) and at third order in benzene, where its value is 0.5t (aromatic). Conjugated isomers of benzene are also considered. The cyclic circulation contributions for an N-membered ring are shown to depend strongly on the molecular graph in which it is embedded. A general expression is found for the cyclic contribution to the pi energy of a ring, the Kekulé graph of which contains N double bonds alternating with N single bonds. It is the energy of the ring, plus the sum of the energies of the N subsystems that result from one double-bond removal, minus the sum of the energies of the N open systems that result from one single-bond cut. This new aromaticity index, ACE(MC), may be seen as the enthalpy of a hyperhomodesmotic chemical equation. In contrast to the index ACE(DC) previously defined from a double cut of the ring, the multiple-cut ACE(MC) exhibits the expected asymptotic disappearance of the cyclic energy as the ring size tends to infinity. In the multiple-cut approach, aromaticity persists in bond-alternating rings, but, in contrast to the total pi energy, the purely cyclic contribution tends to resist distortion. Extension of the approach to charged, branched and heterosubstituted rings are discussed, as well as its ab initio transcription.
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Affiliation(s)
- Jean-Paul Malrieu
- Laboratoire de Chimie et Physique Quantiques, IRSAMC, UMR 5626 CNRS, 118 route de Narbonne, 31062 Toulouse cedex 09, France.
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Angeli C, Malrieu JP. Aromaticity: an ab Initio Evaluation of the Properly Cyclic Delocalization Energy and the π-Delocalization Energy Distortivity of Benzene. J Phys Chem A 2008; 112:11481-6. [DOI: 10.1021/jp805870r] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Celestino Angeli
- Dipartimento di Chimica, Università di Ferrara, Via Borsari 46, I-44100 Ferrara, Italy, and Laboratoire de Chimie et Physique Quantiques, UMR 5625 du CNRS, IRSAMC, Université Paul Sabatier, 118 Rte de Narbonne, 31062 Toulouse, France
| | - Jean-Paul Malrieu
- Dipartimento di Chimica, Università di Ferrara, Via Borsari 46, I-44100 Ferrara, Italy, and Laboratoire de Chimie et Physique Quantiques, UMR 5625 du CNRS, IRSAMC, Université Paul Sabatier, 118 Rte de Narbonne, 31062 Toulouse, France
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Glaser R, Sui Y, Sarkar U, Gates KS. Electronic structures and spin topologies of gamma-picoliniumyl radicals. A study of the homolysis of N-methyl-gamma-picolinium and of benzo-, dibenzo-, and naphthoannulated analogs. J Phys Chem A 2008; 112:4800-14. [PMID: 18494451 PMCID: PMC3311918 DOI: 10.1021/jp8011987] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Radicals resulting from one-electron reduction of (N-methylpyridinium-4-yl) methyl esters have been reported to yield (N-methylpyridinium-4-yl) methyl radical, or N-methyl-gamma-picoliniumyl for short, by heterolytic cleavage of carboxylate. This new reaction could provide the foundation for a new structural class of bioreductively activated, hypoxia-selective antitumor agents. N-methyl-gamma-picoliniumyl radicals are likely to damage DNA by way of H-abstraction and it is of paramount significance to assess their H-abstraction capabilities. In this context, the benzylic C-H homolyses were studied of toluene (T), gamma-picoline (P, 4-methylpyridine), and N-methyl-gamma-picolinium (1c, 1,4-dimethylpyridinium). With a view to providing capacity for DNA intercalation the properties also were examined of the annulated derivatives 2c (1,4-dimethylquinolinium), 3c (9,10-dimethylacridinium), and 4c (1,4-dimethylbenzo[g]quinolinium). The benzylic C-H homolyses were studied with density functional theory (DFT), perturbation theory (up to MP4SDTQ), and configuration interaction methods (QCISD(T), CCSD(T)). Although there are many similarities between the results obtained here with DFT and CI theory, a number of significant differences occur and these are shown to be caused by methodological differences in the spin density distributions of the radicals. The quality of the wave functions is established by demonstration of internal consistencies and with reference to a number of observable quantities. The analysis of spin polarization emphasizes the need for a clear distinction between "electron delocalization" and "spin delocalization" in annulated radicals. Aside from their relevance for the rational design of new antitumor drugs, the conceptional insights presented here also will inform the understanding of ferromagnetic materials, of spin-based signaling processes, and of spin topologies in metalloenzymes.
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Affiliation(s)
- Rainer Glaser
- Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211
| | - Yongqiang Sui
- Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211
| | - Ujjal Sarkar
- Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211
| | - Kent S. Gates
- Department of Chemistry, University of Missouri-Columbia, Columbia, Missouri 65211
- Department of Biochemistry, University of Missouri-Columbia, Columbia, Missouri 65211
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15
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Geier J. Radial Exchange Density and Electron Delocalization in Molecules. J Phys Chem A 2008; 112:5187-97. [DOI: 10.1021/jp800202w] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Affiliation(s)
- Jens Geier
- Albert-Ludwigs-Universität, Institut für Organische Chemie und Biochemie, Albertstraβe 21, D-79104 Freiburg i. Br., Germany
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Gicquel M, Heully JL, Lepetit C, Chauvin R. Carbo-[3]oxocarbon and its isomers: evaluation of the stability and of the electron delocalization. Phys Chem Chem Phys 2008; 10:3578-89. [DOI: 10.1039/b718817j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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17
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Sui Y, Glaser R, Sarkar U, Gates K. Stabilities and Spin Distributions of Benzannulated Benzyl Radicals. J Chem Theory Comput 2007; 3:1091-9. [DOI: 10.1021/ct700051j] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Affiliation(s)
- Yongqiang Sui
- Departments of Chemistry and Biochemistry, University of MissouriColumbia, Columbia, Missouri 65211
| | - Rainer Glaser
- Departments of Chemistry and Biochemistry, University of MissouriColumbia, Columbia, Missouri 65211
| | - Ujjal Sarkar
- Departments of Chemistry and Biochemistry, University of MissouriColumbia, Columbia, Missouri 65211
| | - Kent Gates
- Departments of Chemistry and Biochemistry, University of MissouriColumbia, Columbia, Missouri 65211
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18
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Breher F. Stretching bonds in main group element compounds—Borderlines between biradicals and closed-shell species. Coord Chem Rev 2007. [DOI: 10.1016/j.ccr.2006.09.007] [Citation(s) in RCA: 271] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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19
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Are nucleus-independent (NICS) and 1H NMR chemical shifts good indicators of aromaticity in π-stacked polyfluorenes? Chem Phys Lett 2006. [DOI: 10.1016/j.cplett.2006.06.109] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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20
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Havenith RWA. Electric and Magnetic Properties Computed for Valence Bond Structures: Is There a Link between Pauling Resonance Energy and Ring Current? J Org Chem 2006; 71:3559-63. [PMID: 16626141 DOI: 10.1021/jo060249k] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To establish the link between the aromaticity descriptors based on the Pauling resonance energy and the molecular properties, the electric (polarizability) and magnetic (magnetizability) field response properties have been calculated using the valence bond approach for various molecules and their individual Kekulé resonance structures. The results show that there is no direct relationship between the Pauling resonance energy and the properties; the response properties are weighted averages of the properties of the individual structures. According to the aromaticity criteria based on molecular properties, one-structure benzene would be aromatic; thus, concerning molecular properties, spin-coupled bonds do not behave like localized bonds in Lewis structures, with which they are usually associated.
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Affiliation(s)
- Remco W A Havenith
- Debye Institute, Theoretical Chemistry Group, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
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21
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Malrieu JP, Robert V. Evaluation of the aromatic contribution to the energy of periodic lattices. J PHYS ORG CHEM 2006. [DOI: 10.1002/poc.992] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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22
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Krygowski TM, Stepień BT. Sigma- and pi-electron delocalization: focus on substituent effects. Chem Rev 2005; 105:3482-512. [PMID: 16218559 DOI: 10.1021/cr030081s] [Citation(s) in RCA: 266] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
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Cyrański MK. Energetic aspects of cyclic pi-electron delocalization: evaluation of the methods of estimating aromatic stabilization energies. Chem Rev 2005; 105:3773-811. [PMID: 16218567 DOI: 10.1021/cr0300845] [Citation(s) in RCA: 468] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Mills NS, Tirla C, Benish MA, Rakowitz AJ, Bebell LM, Hurd CMM, Bria ALM. Dications of Fluorenylidenes. The Relationship between Redox Potentials and Antiaromaticity for Meta- and Para-Substituted Diphenylmethylidenefluorenes. J Org Chem 2005; 70:10709-16. [PMID: 16355989 DOI: 10.1021/jo051599u] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
[reaction: see text] Electrochemical oxidation of meta-substituted diphenylmethylidenefluorenes (3a-g) results in the formation of fluorenylidene dications that are shown to be antiaromatic through calculation of the nucleus independent chemical shift (NICS) for the 5- and 6-membered rings of the fluorenyl system. There is a strong linear correlation between the redox potential for the dication and both the calculated NICS and sigma(m). Redox potentials for formation of dications of analogously substituted tetraphenylethylenes shows that, with the exception of the p-methyl derivative, the redox potentials for these dications are less positive than for formation of the dications of 3a-g and for dications of p-substituted diphenylmethylidenefluorenes, 2a-g. The greater instability of dications of 2a-g and 3a-g compared to the reference system implies their antiaromaticity, which is supported by the positive NICS values. The redox potentials for formation of the dications of meta-substituted diphenylmethylidenes (3a-g) are more positive than for the formation of dications of para-substituted diphenylmethylidenes (2a-g), indicating their greater thermodynamic instability. The NICS values for dications of 3a-g are more antiaromatic than for dications of 2a-g, which is consistent with their greater instability of the dications of 3a-g. Although the substituted diphenylmethyl systems are not able to interact with the fluorenyl system through resonance because of their geometry, they are able to moderate the antiaromaticity of the fluorenyl cationic system. Two models have been suggested for this interaction, sigma to p donation and the ability of the charge on the substituted ring system to affect delocalization. Examination of bond lengths shows very limited variation, which argues against sigma to p donation in these systems. A strong correlation between NICS and sigma constants suggests that factors that affect the magnitude of the charge on the benzylic (alpha) carbon of the diphenylmethyl cation affect the antiaromaticity of the fluorenyl cation. Calculated atomic charges on carbons 1-8 and 10-13 show an increase in positive charge, and therefore greater delocalization of charge in the fluorenyl system, with increasing electronegativity of the substituent. The change in the amount of positive charge correlated strongly with NICS, supporting the model in which the amount of delocalization of charge is related to the antiaromaticity of the species. Thus, both aromatic and antiaromatic species are characterized by extensive delocalization of electron density.
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Affiliation(s)
- Nancy S Mills
- Department of Chemistry, Trinity University, One Trinity Place, San Antonio, Texas 78212-7200, USA.
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Some answers to frequently asked questions about the distortive tendencies of π-electronic system. Theor Chem Acc 2005. [DOI: 10.1007/s00214-005-0658-8] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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