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Revisiting Aromaticity and Chemical Bonding of Fluorinated Benzene Derivatives.

Torres-Vega JJ, Vásquez-Espinal A, Ruiz L, Fernández-Herrera MA, Alvarez-Thon L, Merino G, Tiznado W - ChemistryOpen (2015)

Bottom Line: According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region.The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives.These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6-n)F n , where n=1-5).

View Article: PubMed Central - PubMed

Affiliation: Doctorado en Fisicoquímica Molecular, Facultad de Ciencias Exactas, Universidad Andres Bello República 275, Santiago, Chile.

ABSTRACT
The electron delocalization of benzene (C6H6) and hexafluorobenzene (C6F6) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Å above the ring center correlates well (R (2)>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6-n)F n , where n=1-5).

No MeSH data available.


The a) σ-bonding pattern and b) π-bonding pattern of benzene according to AdNDP.
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fig05: The a) σ-bonding pattern and b) π-bonding pattern of benzene according to AdNDP.

Mentions: Let us compare the bonding in benzene and hexafluorobenzene using AdNDP. In benzene, the σ electrons are localized in two sets of two-center two-electron (2 c–2 e) bonds (Figure 5 a), and the π electrons are distributed in three completely delocalized 6 c–2 e bonds (Figure 5 b), as expected.11 In the case of hexafluorobenzene, 24 electrons are localized in twelve in-plane σ lone pairs (σ-LPs). The σ skeleton is comprised by six 2 c–2 e C−F bonds and six 2 c–2 e C−C bonds (Figure 6 a). Remarkably, AdNDP provides two solutions to localize the π bonding in hexafluorobenzene. The first solution includes six pz-LPs (ON=1.92/e/) on the fluorine atoms and three 6 c–2 e bonds (ON=2.00/e/) distributed on the C6 fragment (Figure 6 b). The second solution involves six 2 c–2 e C−F π bonds (ON=2.00/e/) and three 12 c–2 e π bonds (ON=2.00/e/) (Figure 6 c). While both solutions are viable, given that the second option completely localizes the π electrons, we consider this to be the most appropriate localization scheme.


Revisiting Aromaticity and Chemical Bonding of Fluorinated Benzene Derivatives.

Torres-Vega JJ, Vásquez-Espinal A, Ruiz L, Fernández-Herrera MA, Alvarez-Thon L, Merino G, Tiznado W - ChemistryOpen (2015)

The a) σ-bonding pattern and b) π-bonding pattern of benzene according to AdNDP.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4522180&req=5

fig05: The a) σ-bonding pattern and b) π-bonding pattern of benzene according to AdNDP.
Mentions: Let us compare the bonding in benzene and hexafluorobenzene using AdNDP. In benzene, the σ electrons are localized in two sets of two-center two-electron (2 c–2 e) bonds (Figure 5 a), and the π electrons are distributed in three completely delocalized 6 c–2 e bonds (Figure 5 b), as expected.11 In the case of hexafluorobenzene, 24 electrons are localized in twelve in-plane σ lone pairs (σ-LPs). The σ skeleton is comprised by six 2 c–2 e C−F bonds and six 2 c–2 e C−C bonds (Figure 6 a). Remarkably, AdNDP provides two solutions to localize the π bonding in hexafluorobenzene. The first solution includes six pz-LPs (ON=1.92/e/) on the fluorine atoms and three 6 c–2 e bonds (ON=2.00/e/) distributed on the C6 fragment (Figure 6 b). The second solution involves six 2 c–2 e C−F π bonds (ON=2.00/e/) and three 12 c–2 e π bonds (ON=2.00/e/) (Figure 6 c). While both solutions are viable, given that the second option completely localizes the π electrons, we consider this to be the most appropriate localization scheme.

Bottom Line: According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region.The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives.These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6-n)F n , where n=1-5).

View Article: PubMed Central - PubMed

Affiliation: Doctorado en Fisicoquímica Molecular, Facultad de Ciencias Exactas, Universidad Andres Bello República 275, Santiago, Chile.

ABSTRACT
The electron delocalization of benzene (C6H6) and hexafluorobenzene (C6F6) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Å above the ring center correlates well (R (2)>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6-n)F n , where n=1-5).

No MeSH data available.