501
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Cyrański MK, Schleyer PVR, Krygowski TM, Jiao H, Hohlneicher G. Facts and artifacts about aromatic stability estimation. Tetrahedron 2003. [DOI: 10.1016/s0040-4020(03)00137-6] [Citation(s) in RCA: 117] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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502
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Fishtik I, Datta R, Liebman JF. Response Reactions: A Mathematical Well-Defined Way to Obtain Accurate Thermochemistry from ab Initio Calculations. J Phys Chem A 2003. [DOI: 10.1021/jp027089a] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Ilie Fishtik
- Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts 01609-2280, and Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, Maryland 21250
| | - Ravindra Datta
- Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts 01609-2280, and Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, Maryland 21250
| | - Joel F. Liebman
- Department of Chemical Engineering, Worcester Polytechnic Institute, Worcester, Massachusetts 01609-2280, and Department of Chemistry and Biochemistry, University of Maryland, Baltimore County, Baltimore, Maryland 21250
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503
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Bari? D, Maksi? ZB. Non-additivity of the static correlation energy of ?-electrons in planar molecules as a manifestation of anti/aromaticity. J PHYS ORG CHEM 2003. [DOI: 10.1002/poc.666] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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504
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St?pie? BT, Krygowski TM, Cyra?ski MK. Variation of the ?-electron delocalization in exocyclically substituted heptafulvene derivatives. J PHYS ORG CHEM 2003. [DOI: 10.1002/poc.605] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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505
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Shurki A, Hiberty PC, Dijkstra F, Shaik S. Aromaticity and antiaromaticity: what role do ionic configurations play in delocalization and induction of magnetic properties? J PHYS ORG CHEM 2003. [DOI: 10.1002/poc.658] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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506
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Zhan CG, Zheng F, Dixon DA. Electron affinities of Al(n) clusters and multiple-fold aromaticity of the square Al4(2-) structure. J Am Chem Soc 2002; 124:14795-803. [PMID: 12465993 DOI: 10.1021/ja021026o] [Citation(s) in RCA: 156] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The concept of aromaticity was first invented to account for the unusual stability of planar organic molecules with 4n + 2 delocalized pi electrons. Recent photoelectron spectroscopy experiments on all-metal MAl(4)(-) systems with an approximate square planar Al(4)(2-) unit and an alkali metal led to the suggestion that Al(4)(2-) is aromatic. The square Al(4)(2-) structure was recognized as the prototype of a new family of aromatic molecules. High-level ab initio calculations based on extrapolating CCSD(T)/aug-cc-pVxZ (x = D, T, and Q) to the complete basis set limit were used to calculate the first electron affinities of Al(n)(), n = 0-4. The calculated electron affinities, 0.41 eV (n = 0), 1.51 eV (n = 1), 1.89 eV (n = 3), and 2.18 eV (n = 4), are all in excellent agreement with available experimental data. On the basis of the high-level ab initio quantum chemical calculations, we can estimate the resonance energy and show that it is quite large, large enough to stabilize Al(4)(2-) with respect to Al(4). Analysis of the calculated results shows that the aromaticity of Al(4)(2-) is unusual and different from that of C(6)H(6). Particularly, compared to the usual (1-fold) pi aromaticity in C(6)H(6), which may be represented by two Kekulé structures sharing a common sigma bond framework, the square Al(4)(2-) structure has an unusual "multiple-fold" aromaticity determined by three independent delocalized (pi and sigma) bonding systems, each of which satisfies the 4n + 2 electron counting rule, leading to a total of 4 x 4 x 4 = 64 potential resonating Kekulé-like structures without a common sigma frame. We also discuss the 2-fold aromaticity (pi plus sigma) of the Al(3)(-) anion, which can be represented by 3 x 3 = 9 potential resonating Kekulé-like structures, each with two localized chemical bonds. These results lead us to suggest a general approach (applicable to both organic and inorganic molecules) for examining delocalized chemical bonding. The possible electronic contribution to the aromaticity of a molecule should not be limited to only one particular delocalized bonding system satisfying a certain electron counting rule of aromaticity. More than one independent delocalized bonding system can simultaneously satisfy the electron counting rule of aromaticity, and therefore, a molecular structure could have multiple-fold aromaticity.
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Affiliation(s)
- Chang-Guo Zhan
- Department of Medicine, College of Physician & Surgeons, Columbia University, New York, New York 10032, USA.
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507
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Woodcock HL, Schaefer HF, Schreiner PR. Problematic Energy Differences between Cumulenes and Poly-ynes: Does This Point to a Systematic Improvement of Density Functional Theory? J Phys Chem A 2002. [DOI: 10.1021/jp0212895] [Citation(s) in RCA: 166] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- H. Lee Woodcock
- Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602-2525, and Department of Chemistry, University of Georgia, Athens, Georgia 30602
| | - Henry F. Schaefer
- Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602-2525, and Department of Chemistry, University of Georgia, Athens, Georgia 30602
| | - Peter R. Schreiner
- Center for Computational Quantum Chemistry, University of Georgia, Athens, Georgia 30602-2525, and Department of Chemistry, University of Georgia, Athens, Georgia 30602
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508
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Ring Currents and Magnetic Properties of s-Indacene, an Archetypal Paratropic, Non-Antiaromatic Molecule. J Phys Chem A 2002. [DOI: 10.1021/jp0263267] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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509
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De Proft F, von Ragué Schleyer P, van Lenthe JH, Stahl F, Geerlings P. Magnetic properties and aromaticity of o-, m-, and p-benzyne. Chemistry 2002; 8:3402-10. [PMID: 12203320 DOI: 10.1002/1521-3765(20020802)8:15<3402::aid-chem3402>3.0.co;2-6] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
The relative aromaticities of the three singlet benzyne isomers, 1,2-, 1,3-, and 1,4-didehydrobenzenes have been evaluated with a series of aromaticity indicators, including magnetic susceptibility anisotropies and exaltations, nucleus-independent chemical shifts (NICS), and aromatic stabilization energies (all evaluated at the DFT level), as well as valence-bond Pauling resonance energies. Most of the criteria point to the o-benzyne<m-benzyne<p-benzyne aromaticity order, whereas the relative aromaticity of each isomer with respect to benzene depends on the aromaticity criterion. An additional aromaticity evaluation involved the transition state of the Bergman cyclization of (Z)-hexa-1,5-diyn-3-ene which yields p-benzyne. Dissected NICS calculations reveal an aromatic transition state with a larger total NICS but a smaller NICS(pi) component and thus lower aromaticity than benzene.
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Affiliation(s)
- Frank De Proft
- Eenheid Algemene Chemie, Vrije Universiteit Brussel Faculteit Wetenschappen, Pleinlaan 2, 1050 Brussel, Belgium
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510
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Yang SM, Shie JJ, Fang JM, Nandy SK, Chang HY, Lu SH, Wang G. Synthesis of polysubstituted benzothiophenes and sulfur-containing polycyclic aromatic compounds via samarium diiodide promoted three-component coupling reactions of thiophene-2-carboxylate. J Org Chem 2002; 67:5208-15. [PMID: 12126408 DOI: 10.1021/jo0257849] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
By the promotion of samarium diiodide, thiophene-2-carboxylate reacted with 2 equiv of ketones at the C-4 and C-5 positions to give diols such as 2 and 9. Because the intermediary organosamarium species were oxophilic but not too basic, the double hydroxyalkylations with various ketone substrates, including alkyl aryl ketones, acetylthiophenes, cyclohexanone, alpha-tetralone, and alpha-phenylacetophenones, were realized without complication of side reactions. The diol products underwent an acid-catalyzed dehydration to give dienes such as 3 and 10, which were treated with DDQ to give either polysubstituted thiophenes (e.g., 4 and 11) or benzothiophenes (e.g., 5, 13, and 14) depending on the reaction conditions. Oxidative annulations of 4,5-diarylthiophenes 11 and 4,5,6,7-tetraphenylbenzothiophenes 14 were carried out by photochemical or chemical methods to give the sulfur-containing polycyclic aromatic compounds, such as phenanthro[9,10-b]thiophene-2-carboxylate, piceno[13,14-b]thiophene-2-carboxylate, and tribenzo[fg,ij,rst]pentapheno[15,16-b]thiophene-2-carboxylates. This method is applicable to the preparation of polysubstituted thiophenes, benzothiophenes, and the related compounds possessing liquid crystalline, photochromic, and other functional properties.
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Affiliation(s)
- Shyh-Ming Yang
- Department of Chemistry, National Taiwan University, Taipei 106, Taiwan, Republic of China
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511
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Alkorta I, Rozas I, Elguero J. Interaction of anions with perfluoro aromatic compounds. J Am Chem Soc 2002; 124:8593-8. [PMID: 12121100 DOI: 10.1021/ja025693t] [Citation(s) in RCA: 424] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The complexes formed by a variety of anions with perfluoro derivatives of benzene, naphthalene, pyridine, thiophene, and furan have been calculated using DFT (B3LYP/6-31++G**) and MP2 (MP2/6-31++G** and MP2/6-311++G**) ab initio methods. The minimum structures show the anion interacting with the pi-cloud of the aromatic compounds. The interaction energies obtained range between -8 and -19 kcal mol(-1). The results obtained at the MP2/6-31++G** and MP2/6-311++G** levels are similar. However, the B3LYP/6-31++G** results provide longer interaction distances and smaller interaction energies than do the MP2 results. The interaction energies have been partitioned using an electrostatic, polarization, and van der Waals scheme. The AIM analysis of the electron density shows a variety of topologies depending on the aromatic system considered.
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Affiliation(s)
- Ibon Alkorta
- Instituto de Química Médica (C.S.I.C.), Juan de la Cierva, 3, 28006-Madrid, Spain.
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512
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513
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Affiliation(s)
- Ralf I Kaiser
- Department of Chemistry University of York York YO10 5DD, UK.
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514
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Leach AG, Catak S, Houk KN. Mechanism of the forbidden [3s,5s]-sigmatropic shift: orbital symmetry influences stepwise mechanisms involving diradical intermediates. Chemistry 2002; 8:1290-9. [PMID: 11921212 DOI: 10.1002/1521-3765(20020315)8:6<1290::aid-chem1290>3.0.co;2-k] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The mechanisms of [3s,5s]-sigmatropic shifts of octa-1,3,7-triene and 7-methylenenona-1,3,8-triene have been elaborated using B3LYP and BPW91 density functional theory and CASPT2 methods. These orbital symmetry forbidden rearrangements are stepwise, involving diradical intermediates. A comparison with several [3,3]-sigmatropic shifts of substituted hexadienes and of [5,5]-sigmatropic shifts that are allowed, but nevertheless follow stepwise paths, shows that the activation barrier for the disallowed [3,5] shift is significantly larger than that for the stepwise reactions that are orbital symmetry allowed. Cyclic diradicals that have an aromatic circuit of electrons including the two radical centers and conjugated pi or sigma bonds are stabilized as compared to cyclic diradicals with an antiaromatic circuit of electrons. This applies to the transition states leading to and from the diradicals and influences the activation energies of stepwise sigmatropic shifts. The magnitudes of these effects are small but will have a significant influence on the rates of competing processes. This series of calculations has been used to assess the relative capabilities of the two functionals. We find that BPW91 underestimates the endothermicity of diradical formation and the barrier to diradical formation whereas B3LYP overestimates these quantities.
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Affiliation(s)
- Andrew G Leach
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA
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515
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Cyrañski MK, Krygowski TM, Katritzky AR, Schleyer PVR. To what extent can aromaticity be defined uniquely? J Org Chem 2002; 67:1333-8. [PMID: 11846683 DOI: 10.1021/jo016255s] [Citation(s) in RCA: 543] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Statistical analyses of quantitative definitions of aromaticity, ASE (aromatic stabilization energies), RE (resonance energies), Lambda (magnetic susceptibility exaltation), NICS, HOMA, I5, and A(J), evaluated for a set of 75 five-membered pi-electron systems: aza and phospha derivatives of furan, thiophene, pyrrole, and phosphole (aromatic systems), and a set of 30 ring-monosubstituted compounds (aromatic, nonaromatic, and antiaromatic systems) revealed statistically significant correlations among the various aromaticity criteria, provided the whole set of compounds is involved. Hence, broadly considered, the various manifestations of aromaticity are related and aromaticity can be regarded statistically as a one-dimensional phenomenon. In contrast, when comparisons are restricted to some regions or groups of compounds, e.g., aromatic compounds with ASE > 5 kcal/mol or polyhetero-five-membered rings, the quality of the correlations can deteriorate or even vanish. In practical applications, energetic, geometric, and magnetic desriptors of aromaticity do not speak with the same voice. Thus, in this sense, the phenomenon of aromaticity is regarded as being statistically multidimensional.
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Affiliation(s)
- Michal K Cyrañski
- Department of Chemistry, University of Warsaw, Pasteura 1, 02 093 Warsaw, Poland.
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516
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Stȩpień BT, Cyrański MK, Krygowski TM. Aromaticity strongly affected by substituents in fulvene and heptafulvene as a new method of estimating the resonance effect. Chem Phys Lett 2001. [DOI: 10.1016/s0009-2614(01)01320-3] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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517
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Shiota Y, Kondo M, Yoshizawa K. Role of molecular distortions in the spin–orbit coupling between the singlet and triplet states of the 4π electron systems C4H4, C5H5+, and C3H3−. J Chem Phys 2001. [DOI: 10.1063/1.1412250] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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518
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519
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520
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Aromaticity of dihetero analogues of pentalene dianion. X-Ray and ab initio studies of eight methyl furo[3,2- b ]pyrrole-5-carboxylate derivatives and five methyl furo[2,3- b ]pyrrole-5-carboxylate derivatives. Tetrahedron 2001. [DOI: 10.1016/s0040-4020(01)00854-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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