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Aromatic properties of 8-hydroxyquinoline and its metal complexes

100%
Zborowski K., Solá M., Poater J., Proniewicz L.
Open Chemistry
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2013
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vol. 11
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issue 5
655-663
EN
Chelatoaromaticity (aromaticity of chelate complexes) has been recently recognized as an important property influencing the stability of chelate compounds. In this paper, aromaticity of various forms of 8-hydroxyquinoline (anion, neutral molecule, zwitterion and cation) as well as its chelate complexes with magnesium and aluminium ions are investigated. Aromatic properties of these compounds are analyzed using several aromaticity indices based on energetic, geometric, magnetic and electronic physical manifestations of this phenomenon. Results of performed calculations have shown different aromatic properties for the two rings (pyridine and benzene) occurring in the studied ligand. Aromaticity of these rings in metal complexes of 8-hydroxyquinoline is significantly higher than that in corresponding ligand anion. This means that during complexation the aromaticity of the ligand increases and the chelatoaromatic effect stabilizes the studied metal complexes. In contrast, metallocyclic rings of studied metal complexes have non-aromatic properties, and, consequently, the metallocyclic ring is not stabilized by chelatoaromaticity. We conclude that, in the complex, every 8-hydroxyquinoline unit and the metal ion are separated p-electronic systems. [...]
2
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Theoretical studies on the electronic structures and spectra of single silicon-doped SWCNTs

88%
Gao P., Yu Y., Ni Z., Teng Q.
Open Chemistry
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2010
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vol. 8
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issue 3
587-593
EN
The equilibrium geometries and electronic structures of a series of SWCNTs doped with a silicon atom were studied by using density function theory (DFT). The most stable doping site of silicon predicted at B3LYP/6-31G(d,p) level was located near the boundary of the SWCNTs. The energy gaps of (3,3) C48, (3,3) C60 and (3,3) C72 were respectively decreased by 0.43, 0.25 and 0.14 eV after doping. Based on the B3LYP/6-31G(d) optimized geometries, the electronic spectra of the doped SWCNTs were computed using the INDO/CIS method. The first UV absorption at 973.9 nm of (5,5)-Si(L) (C59Si) compared with that at 937.5 nm of (5,5) (C60) was red-shifted. The 13C NMR spectra and nuclear independent chemical shifts (NICS) of the doped SWCNTs were investigated at B3LYP/6-31G(d) level. The chemical shift at 119.4 of the carbon atom bonded with the silicon atom in (3,3)-Si(L) (C59Si) in comparison with that at 144.1 of the same carbon atom in (3,3) (C60) moved upfield. The tendency of the aromaticity (NICS = −0.1) for (3,3)-Si(H) (C47Si) with respect to that of the anti-aromaticity (NICS = 6.0) for (3,3) (C48) was predicted. [...]
3
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NBO and NICS analysis of the allylic rearrangements (the Cope and 3-aza-Cope rearrangements) of hexa-1,5-diene and N-vinylprop-2-en-1-amine: A DFT study

88%
Zahedi E., Ali-Asgari S., Keley V.
Open Chemistry
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2010
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vol. 8
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issue 5
1097-1104
EN
In this work, ab initio density functional theory (DFT) calculations have been performed on the 3,3-sigmatropic rearrangements of hexa-1,5-diene (Cope) and N-vinylprop-2-en-1-amine (3-aza-Cope) in the gas phase. The barrier heights and heats of reactions calculated at the B3LYP/6-311G** level of theory were in good agreement with experimental data. Transition states optimized with B3LYP/6-311G** theory were used for calculating the nucleus independent chemical shift (NICS) and, a natural bond orbital (NBO) analysis was also performed at the same level of theory. Our results indicate that the aromaticities of the transition states are controlled by the out-of-plane component and that the chair-like transition state of the Cope rearrangement exhibits the strongest aromatic character. Analysis of donor-acceptor (bonding and anti-bonding) interactions of σ3–4 → π*1–2 suggests that the TS structure in the hexa-1,5-diene reaction (the Cope rearrangement) has more aromatic character than the N-vinylprop-2-en-1-amine reaction (the 3-aza-Cope rearrangement). The NBO results show that in the hexa-1,5-diene and N-vinylprop-2-en-1-amine rearrangements, activation energies are controlled by σ3–4 → π*1–2 and σ3–4 → π*1–2 resonance energies. [...]
4
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Fullerenes patched by flowers with octagonal core

88%
Pop R., Medeleanu M., Diudea M., Szefler B., Cioslowski J.
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issue 1
90-97
EN
The aromatic character of three different flowers of general formula [n:(p i,p j)n/2], namely [8:(5,7)4], [8:(6,6)4] and [8:(5,6)4], has been evaluated by means of geometric (HOMA index), energetic (heats of formation) and magnetic criteria (NICS index, exaltation of magnetic susceptibility). Also, the reactivity descriptors within the DFT approach -absolute hardness, electrophilicity, Fukui functions - have been computed. All the different methods used for estimating the aromaticity led to a unitary conclusion. Two fullerene structures, patched by the most stable 8-Sumanene flower, have been designed and evaluated by means of ab initio computations [...]
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