Computed NMR shielding increments over benzo-analogs of unsaturated five-membered ring heterocyclic compounds as a measure of aromaticity

Martin, Ned H.; Rowe, Jimmy E.; Pittman, Eddie LaReece

doi:10.1016/j.jmgm.2010.01.005

Cited by 12 publications

(7 citation statements)

References 34 publications

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“…The anions (11)(12)(13)(14) cause electrostatic deshielding of the probe, somewhat offsetting the shielding effect of aromaticity. The cations (15)(16)(17) cause electrostatic shielding of the probe, thus enhancing the shielding effect of due to aromaticity.…”

Section: Benzene Fused To Tropylium Ionmentioning

confidence: 99%

“…A molecular probe of shielding effects has been useful for distinguishing between aromatic and antiaromatic systems [14], and good correlations have been obtained between shielding effects on a molecular probe and other measures of aromaticity in heterocyclic systems [15,16]. Furthermore, use of a molecular probe allows prediction of chemical shift effects on protons as a function of their position over the ring in question.…”

Section: Introductionmentioning

confidence: 99%

“…Figure 2. Structures of the fused benzene-ionic aromatic hydrocarbons and their parent ionic aromatic hydrocarbons in the study (11)(12)(13)(14)(15)(16)(17). Computed natural population analysis charges (in e) of the carbon atoms are indicated.…”

Section: Introductionmentioning

confidence: 99%

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Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

Martin¹,

Teague²,

Mills³

2010

Symmetry

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Through-space isotropic NMR shielding values of a perpendicular diatomic hydrogen probe moved in a 0.5 Å grid 2.5 Å above several polycyclic aromatic/antiaromatic ring and aromatic/aromatic hydrocarbons were computed with Gaussian 03 at the GIAO HF/6-31G(d,p) level. Combinations of benzene fused with cyclobutadiene, with the tropylium ion, and with the cyclopentadienyl anion were investigated. Subtraction of the isolated H 2 isotropic value gave shielding increments (∆σ), which, when plotted against Cartesian coordinates of the probe over each hydrocarbon, gave representations of threedimensional isotropic shielding increment surfaces. The results are related to the degree of bond length alternation, the extent of π electron delocalization, and (for the ions) the NPA charge distribution. The shielding increment data are compared to NICS(1) values computed at the same level; both indicate the degree of aromaticity or antiaromaticity of the component rings.

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Section: Benzene Fused To Tropylium Ionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

Martin¹,

Teague²,

Mills³

2010

Symmetry

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“…[14] Accordingly, indole shows the largest aromaticity at the 5-membered heteroaromatic ring among benzofuran, benzothiophene, and indole. [15,16] In addition, an inherently strong endocyclic C N bond obviously increases the difficulty in breaking an indole core. To achieve aromatic metamorphosis of indoles via the cleavage of the endocyclic C N bonds, a more powerful strategy should be utilized.…”

Section: Aromatic Metamorphosis Of Indoles Through Electron Injection...mentioning

confidence: 99%

Electron injection for aromatic metamorphosis of indole

Yorimitsu

2020

J Chinese Chemical Soc

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Aromatic metamorphosis, endocyclic transformations of aromatic compounds, has been emerging as a new synthetic strategy in organic synthesis. This counterintuitive strategy necessitates very powerful reactions that can surmount aromaticity and the strong carbon–heteroatom bonds of the heteroaromatic rings. This Short Account describes the development of the currently most powerful elementary reaction for aromatic metamorphosis, which is electron injection from lithium metal. Exceptionally robust and aromatic N‐phenylindole is subjected to the electron injection, resulting in the formation of the corresponding dianionic intermediate through reductive ring‐opening. A trapping reaction of the dianionic intermediate with organoboronic acid pinacol esters provides benzazaborines, which are attractive BN‐isosteres of naphthalenes. The electron injection helps establishing aromatic metamorphosis as a reliable synthetic methodology to provide novel useful molecules.

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“…However, despite the fact that magnetically induced methods are directly related to aromaticity descriptions, the relationship between the latter and electron delocalisation can be argued . Finally, some techniques have also been developed to describe NICS values within a 3D molecular space, such as those developed by Kleinpeter et al, Martin et al., Rodríguez‐Otero et al . and Sebastiani and Parker .…”

Section: Introductionmentioning

confidence: 99%

A Study of π–π Stacking Interactions and Aromaticity in Polycyclic Aromatic Hydrocarbon/Nucleobase Complexes

Trujillo

Sánchez‐Sanz

2015

ChemPhysChem

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We analysed the interactions and aromaticity electron-density delocalisation observed in π-π complexes between the phenalenyl radical and acenaphthylene, and the DNA and RNA nucleobases (adenine, guanine, cytosine, thymine and uracil). Interaction energies are obtained at the M06-2X/6-311++G(2df,p) computational level for gas phase and PCM-water conditions. For both the phenalenyl radical and acenaphthylene, the complexes formed with guanine are the most stable ones. Atoms in molecules and natural bond orbital results reveal weak π-π interactions between both interacting moieties, characterized by bond critical points between C⋅⋅⋅C and C⋅⋅⋅N atoms. Nucleus independent chemical shifts (NICS) indicate the retention of the aromatic character of the monomers in the outer region of the complex. The fluctuation indexes reveal a loss of electron delocalisation upon complexation for all cases except guanine complexes. Nevertheless, the interface region shows large negative NICS values, which is not associated with an increase of the aromaticity or electron-density delocalisation, but with magnetic couplings of both molecules, leading to an unrealistic description of the aromatic behaviour in that region.

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Computed NMR shielding increments over benzo-analogs of unsaturated five-membered ring heterocyclic compounds as a measure of aromaticity

Cited by 12 publications

References 34 publications

Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

Computed NMR Shielding Effects over Fused Aromatic / Antiaromatic Hydrocarbons

Electron injection for aromatic metamorphosis of indole

A Study of π–π Stacking Interactions and Aromaticity in Polycyclic Aromatic Hydrocarbon/Nucleobase Complexes

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