Aromaticity strongly affected by substituents in fulvene and heptafulvene as a new method of estimating the resonance effect

Stępień, Beata T.; Cyrański, Michał K.; Krygowski, Tadeusz M.

doi:10.1016/s0009-2614(01)01320-3

Cited by 60 publications

(37 citation statements)

References 22 publications

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“…NICS values cannot be used to perform this kind of comparison, since they strongly depend on the area of the ring [53]. When HOMA is applied, it gives −0.286 for fulvene and 0.164 for heptafulvene [6]. In order to investigate this issue at the level of the actual approaches applied to estimate the aromatic stabilization energy, we followed the procedure presented below.…”

Section: Methodsmentioning

confidence: 99%

“…The Hess-Schaad model for estimating the resonance energy per π electron (REPE) [4] gives the same value for fulvene and heptafulvene (REPE = −0.002), indicating that they both possess nonaromatic character. Schleyer's NICS [5] value for heptafulvene is 8.468 [6], clearly indicating its non-or even antiaromatic character. Since heptafulvene has 4N+3 π electrons, it becomes more stable when electron-withdrawing substituents are added to it, allowing the number of π electrons in the ring to approach 4N+2.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, 8,8-diformylheptafulvene is a stable compound with a known crystallographic structure [7] and a high value of the geometry-based aromaticity index HOMA [8,9], 0.769 (based on the experimental geometry) [7,10]. Theoretical studies of 8-substituted heptafulvene derivatives have shown [6] that increasing the electron-accepting power of the substituent leads to an increase in the aromaticity of the ring, as documented by several aromaticity indices [11].…”

Section: Introductionmentioning

confidence: 99%

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Aromatic character of heptafulvene and its complexes with halogen atoms

2011

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Geometry optimization of heptafulvene-halogen complexes (halogens: F, Cl, Br, I, and At) carried out at the B3LYP/6-311+G(d,p) level of theory allowed us to estimate the geometry-based aromaticity index HOMA, the magnetism-based indices NICS, NICS(1), and NICS(1)(ZZ), as well as the energy of complex formation. Application of the NBO method allowed us to estimate the pEDA characteristics of the π-electron distribution in complexes (i.e., the electron excess/deficiency of the π-electron system in the ring). All of the characteristics of the complexes were found to be mutually interrelated, exhibiting good or at least acceptable correlation coefficients. It was also noted that halogen atoms with greater radii yielded weaker complexes and lower aromaticities, as shown by the HOMA, NICS, and pEDA indices. The energy of complex formation was observed to be linearly correlated with the degree of aromatization of the heptafulvene ring, as expressed by these indices.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Aromatic character of heptafulvene and its complexes with halogen atoms

2011

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“…However, the fluoro substituent is known to behave in an unexpected way. [59,60] It is strongly electron accepting and relatively strongly p-electron donating. When F or MeO groups are in the meta position(s), CSF1 changes its sign.…”

Section: Full Papermentioning

confidence: 99%

Factor Analysis of Deuterium Isotope Effects on ¹³C NMR Chemical Shifts in Schiff Bases

Dominiak¹,

Filarowski²,

Hansen³

et al. 2005

Chemistry A European J

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We have analyzed deuterium isotope effects on (13)C chemical shifts in a series of o-hydroxy Schiff bases by applying factor analysis. Two orthogonal factors were obtained that explain about 80 and 10 % of the variance of the data. The numerical values of these factors can be related to 1H NMR chemical shifts of the proton involved in the intramolecular bonds delta(XH) (X = O or N). Such a relation allows one to identify clusters of compounds with different tautomeric forms of hydrogen bonding. Application of a similar approach to solution 13C NMR chemical shifts produces three important factors, which have a different structure to factors describing isotope effects. This illustrates well the different nature of chemical shifts and isotope effects. The three factors explain about 54, 15, and 13 % of variance. They can be rationalized and are strongly related to the electronic properties and location of substituents.

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“…However, when the calculated quantities (e.g., bond lengths) are mixed with the experimental ones, the shortcomings of quantum chemical treatment are bound to resurface. Unfortunately, HOMA is routinely calculated in just such a way: the theoretically obtained bond lengths for a studied system are combined with the parameterization based on experimental geometries of the reference molecules [7,[11][12][13][14][15][16][17][18]. One may have justified suspicions that HOMA computed in such a way would undergo strong changes with a change of the basis set, computational method, or even the exchange-correlation functional of DFT (a great variety of which have been recently developed and presented for general use).…”

Section: Introductionmentioning

confidence: 99%

Avoiding pitfalls of a theoretical approach: the harmonic oscillator measure of aromaticity index from quantum chemistry calculations

2012

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The concept of the harmonic oscillator measure of aromaticity (HOMA) is based on comparing the geometrical parameters of a studied molecule with the parameters for an ideal aromatic system derived from bond lengths of the reference molecules. Nowadays, HOMA is routinely computed combining the geometries from quantum chemistry calculations with the experimentally based parameterization. Thus, obtained values of HOMA, however, are bound to suffer from inaccuracies of the theoretical methods and strongly depend on computational details. This could be avoided by obtaining both the input geometries and the parameters with the same theoretical method, but efficiency of the error compensation achieved in this way has not yet been probed. In our work, we have prepared a benchmark set of HOMA values for 25 cyclic hydrocarbons, based on the all core CCSD(T)/cc-pCVQ(T)Z geometries, and used it to investigate the impact of different choices of the exchangecorrelation functionals and basis sets on HOMA, calculated against the experimentally based (HOMA EP ) or the consistently calculated (HOMA CCP ) parameters. We show that using HOMA EP leads to large and unsystematic errors, and strong sensitivity to the choice of XC functional, basis set, and the experimental data for the reference geometry. This sensitivity is largely, although not completely attenuated in the consistent approach. We recommend the most suitable functionals for calculating HOMA in both approaches (HOMA EP and HOMA CCP ), and provide the HOMA parameters for 25 studied exchange-correlation functionals and two popular basis sets.

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Aromaticity strongly affected by substituents in fulvene and heptafulvene as a new method of estimating the resonance effect

Cited by 60 publications

References 22 publications

Aromatic character of heptafulvene and its complexes with halogen atoms

Aromatic character of heptafulvene and its complexes with halogen atoms

Factor Analysis of Deuterium Isotope Effects on ¹³C NMR Chemical Shifts in Schiff Bases

Avoiding pitfalls of a theoretical approach: the harmonic oscillator measure of aromaticity index from quantum chemistry calculations

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Aromaticity strongly affected by substituents in fulvene and heptafulvene as a new method of estimating the resonance effect

Cited by 60 publications

References 22 publications

Aromatic character of heptafulvene and its complexes with halogen atoms

Aromatic character of heptafulvene and its complexes with halogen atoms

Factor Analysis of Deuterium Isotope Effects on 13C NMR Chemical Shifts in Schiff Bases

Avoiding pitfalls of a theoretical approach: the harmonic oscillator measure of aromaticity index from quantum chemistry calculations

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Factor Analysis of Deuterium Isotope Effects on ¹³C NMR Chemical Shifts in Schiff Bases