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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.


Contour lines of the z-component of the induced magnetic field (Bindz), in a plane perpendicular to the molecule, for benzene (left) and hexafluorobenzene (right). The scale is given in ppm and the spatial scale in Å.
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fig01: Contour lines of the z-component of the induced magnetic field (Bindz), in a plane perpendicular to the molecule, for benzene (left) and hexafluorobenzene (right). The scale is given in ppm and the spatial scale in Å.

Mentions: Figure 1 depicts the contour lines of the z component of the induced magnetic field (Bindz) produced by an applied external magnetic field, perpendicular to the molecular planes of benzene and hexafluorobenzene. The external magnetic field induces a current density around the molecular plane. Clearly, at distances ≤1.0 Å from the ring center, the nuclear and σ contributions are still present in both systems. At distances ≥1.0 Å, a well-defined shielding region (involving the complete ring) emerges. Note that the shielding region of hexafluorobenzene is smaller than that of benzene. The continuous substitution of hydrogen by fluorine in benzene gradually decreases the size of the shielding region (see Figures S1.1–S1.2 in the Supporting Information).


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)

Contour lines of the z-component of the induced magnetic field (Bindz), in a plane perpendicular to the molecule, for benzene (left) and hexafluorobenzene (right). The scale is given in ppm and the spatial scale in Å.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

fig01: Contour lines of the z-component of the induced magnetic field (Bindz), in a plane perpendicular to the molecule, for benzene (left) and hexafluorobenzene (right). The scale is given in ppm and the spatial scale in Å.
Mentions: Figure 1 depicts the contour lines of the z component of the induced magnetic field (Bindz) produced by an applied external magnetic field, perpendicular to the molecular planes of benzene and hexafluorobenzene. The external magnetic field induces a current density around the molecular plane. Clearly, at distances ≤1.0 Å from the ring center, the nuclear and σ contributions are still present in both systems. At distances ≥1.0 Å, a well-defined shielding region (involving the complete ring) emerges. Note that the shielding region of hexafluorobenzene is smaller than that of benzene. The continuous substitution of hydrogen by fluorine in benzene gradually decreases the size of the shielding region (see Figures S1.1–S1.2 in the Supporting Information).

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.