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Highly fluorinated naphthalenes and bifurcated C–H⋯F–C hydrogen bonding
Get PDFThe synthesis and crystal structures of 1,2,4,5,6,8-hexafluoronaphthalene and 1,2,4,6,8-pentafluoronaphthalene are reported. Intermolecular interactions are dominated by offset stacking and by C–H⋯F–C hydrogen bonds. For hexafluoronaphthalene, molecules are linked in layers with (4,4) network topology via R12(6) C–H⋯(F–C)2 supramolecular synthons that are rationalised by consideration of the calculated electrostatic potential of the molecule. Such an arrangement is prevented by the additional hydrogen atom in pentafluoronaphthalene and molecules instead form tapes via an R12(8) (C–H⋯F)2 synthon. The geometric characteristics of C–H⋯(F–C)2 bifurcated hydrogen bonds have been analysed for crystal structures in the Cambridge Structural Database (6416 crystal structures; 9534 C–H⋯(F–C)2 bifurcated hydrogen bonds). A geometric analysis of these hydrogen bonds has enabled the extent of asymmetry of these hydrogen bonds to be assessed and indicates a preference for symmetrically bifurcated interactions
Molecular Tuning of the Closed Shell C–H···F–C Hydrogen Bond
No full textThe existence of the rare six-membered
and intramolecular C–H···F–C
hydrogen-bond has been experimentally proven in the gas phase and
in the solid state recently. However, the effect of the substituents
on this C–H···F–C hydrogen-bond system
has never been reported. In view of the importance of this type of
C–H···F–C H-bonding whose weak interaction
has been found critical in nanotechnology and biological systems,
the nine functional groups composed of electron donating and electron
withdrawing groups are inserted into this C–H···F–C
interaction to study the group effect on the hydrogen bonding. Group
effects on this C–H···F–C H-bonding system
have been found, and their effects on the H-bonding system have been
found to be tunable
C−H···F Interactions in the Crystal Structures of Some Fluorobenzenes
No full textThe existence and nature of C−H···F−C interactions in crystalline fluorobenzenes 1−3 and 7−10
are discussed. These compounds were chosen because they contain only C, H, and F atoms; this is necessary
in the evaluation of the weak acceptor capabilities of the C−F group. All of these compounds are liquids at
room temperature, and single crystals for X-ray diffraction were grown in situ. The analysis of the C−H···F
interactions that are found in all of these crystal structures takes the form of comparisons with related
C−H···O/C−H···N analogues. Fluorobenzene, 1, bears a close relationship to pyridinium fluoride, pyridine
1-oxide, and benzonitrile at the level of individual interactions, showing that the character of the structure-determining intermolecular interactions in these four crystal structures are the same. Similarly, 1,4-difluorobenzene, 3, and 1,4-benzoquinone are related, the C−H···F interactions in the former playing the same structural
role as the C−H···O interactions in the latter. A comparison of 3 with the unsymmetrical 1,4-dihalogenated
benzenes, 4−6 indicates the importance of C−H···F interactions in these structures. With an increase in the
F content of the molecules, the C−H acidity also increases and the C−H···F interactions in 1,3,5-trifluorobenzene, 7, and 1,2,4,5-tetrafluorobenzene, 8, become stronger and more important. Compounds 7 and 8 are
structurally very similar to 1,3,5-triazine and 1,2,4,5-tetrazine, and this similarity further strengthens the argument
that C−H···F interactions resemble C−H···N interactions and provides evidence for their description as weak
hydrogen bonds. 1,2,3,4-Tetrafluorobenzene, 9, is polymorphic but the role of the C−H···F interactions in
the two forms is similar. A comparison of the C−H···F geometries in compounds 1−10 with other C-, H-,
and F-containing compounds in the Cambridge Structural Database reveals that the hydrogen bond properties
are more pronounced in 1−10. It is concluded that only when the carbon acidity is enhanced to the levels of
the compounds in the present study, is the hydrogen-bond nature of the C−H···F interaction even revealed.
This study also demonstrates that the C−F group prefers to form C−H···F interactions rather than F···F contacts.
The behavior of organic fluorine in crystal packing is therefore quite different from the heavier halogens
C−H···F Interactions in the Crystal Structures of Some Fluorobenzenes
No full textThe existence and nature of C−H···F−C interactions in crystalline fluorobenzenes 1−3 and 7−10
are discussed. These compounds were chosen because they contain only C, H, and F atoms; this is necessary
in the evaluation of the weak acceptor capabilities of the C−F group. All of these compounds are liquids at
room temperature, and single crystals for X-ray diffraction were grown in situ. The analysis of the C−H···F
interactions that are found in all of these crystal structures takes the form of comparisons with related
C−H···O/C−H···N analogues. Fluorobenzene, 1, bears a close relationship to pyridinium fluoride, pyridine
1-oxide, and benzonitrile at the level of individual interactions, showing that the character of the structure-determining intermolecular interactions in these four crystal structures are the same. Similarly, 1,4-difluorobenzene, 3, and 1,4-benzoquinone are related, the C−H···F interactions in the former playing the same structural
role as the C−H···O interactions in the latter. A comparison of 3 with the unsymmetrical 1,4-dihalogenated
benzenes, 4−6 indicates the importance of C−H···F interactions in these structures. With an increase in the
F content of the molecules, the C−H acidity also increases and the C−H···F interactions in 1,3,5-trifluorobenzene, 7, and 1,2,4,5-tetrafluorobenzene, 8, become stronger and more important. Compounds 7 and 8 are
structurally very similar to 1,3,5-triazine and 1,2,4,5-tetrazine, and this similarity further strengthens the argument
that C−H···F interactions resemble C−H···N interactions and provides evidence for their description as weak
hydrogen bonds. 1,2,3,4-Tetrafluorobenzene, 9, is polymorphic but the role of the C−H···F interactions in
the two forms is similar. A comparison of the C−H···F geometries in compounds 1−10 with other C-, H-,
and F-containing compounds in the Cambridge Structural Database reveals that the hydrogen bond properties
are more pronounced in 1−10. It is concluded that only when the carbon acidity is enhanced to the levels of
the compounds in the present study, is the hydrogen-bond nature of the C−H···F interaction even revealed.
This study also demonstrates that the C−F group prefers to form C−H···F interactions rather than F···F contacts.
The behavior of organic fluorine in crystal packing is therefore quite different from the heavier halogens
C−H···F Interactions in the Crystal Structures of Some Fluorobenzenes
No full textThe existence and nature of C−H···F−C interactions in crystalline fluorobenzenes 1−3 and 7−10
are discussed. These compounds were chosen because they contain only C, H, and F atoms; this is necessary
in the evaluation of the weak acceptor capabilities of the C−F group. All of these compounds are liquids at
room temperature, and single crystals for X-ray diffraction were grown in situ. The analysis of the C−H···F
interactions that are found in all of these crystal structures takes the form of comparisons with related
C−H···O/C−H···N analogues. Fluorobenzene, 1, bears a close relationship to pyridinium fluoride, pyridine
1-oxide, and benzonitrile at the level of individual interactions, showing that the character of the structure-determining intermolecular interactions in these four crystal structures are the same. Similarly, 1,4-difluorobenzene, 3, and 1,4-benzoquinone are related, the C−H···F interactions in the former playing the same structural
role as the C−H···O interactions in the latter. A comparison of 3 with the unsymmetrical 1,4-dihalogenated
benzenes, 4−6 indicates the importance of C−H···F interactions in these structures. With an increase in the
F content of the molecules, the C−H acidity also increases and the C−H···F interactions in 1,3,5-trifluorobenzene, 7, and 1,2,4,5-tetrafluorobenzene, 8, become stronger and more important. Compounds 7 and 8 are
structurally very similar to 1,3,5-triazine and 1,2,4,5-tetrazine, and this similarity further strengthens the argument
that C−H···F interactions resemble C−H···N interactions and provides evidence for their description as weak
hydrogen bonds. 1,2,3,4-Tetrafluorobenzene, 9, is polymorphic but the role of the C−H···F interactions in
the two forms is similar. A comparison of the C−H···F geometries in compounds 1−10 with other C-, H-,
and F-containing compounds in the Cambridge Structural Database reveals that the hydrogen bond properties
are more pronounced in 1−10. It is concluded that only when the carbon acidity is enhanced to the levels of
the compounds in the present study, is the hydrogen-bond nature of the C−H···F interaction even revealed.
This study also demonstrates that the C−F group prefers to form C−H···F interactions rather than F···F contacts.
The behavior of organic fluorine in crystal packing is therefore quite different from the heavier halogens
C−H···F Interactions in the Crystal Structures of Some Fluorobenzenes
No full textThe existence and nature of C−H···F−C interactions in crystalline fluorobenzenes 1−3 and 7−10
are discussed. These compounds were chosen because they contain only C, H, and F atoms; this is necessary
in the evaluation of the weak acceptor capabilities of the C−F group. All of these compounds are liquids at
room temperature, and single crystals for X-ray diffraction were grown in situ. The analysis of the C−H···F
interactions that are found in all of these crystal structures takes the form of comparisons with related
C−H···O/C−H···N analogues. Fluorobenzene, 1, bears a close relationship to pyridinium fluoride, pyridine
1-oxide, and benzonitrile at the level of individual interactions, showing that the character of the structure-determining intermolecular interactions in these four crystal structures are the same. Similarly, 1,4-difluorobenzene, 3, and 1,4-benzoquinone are related, the C−H···F interactions in the former playing the same structural
role as the C−H···O interactions in the latter. A comparison of 3 with the unsymmetrical 1,4-dihalogenated
benzenes, 4−6 indicates the importance of C−H···F interactions in these structures. With an increase in the
F content of the molecules, the C−H acidity also increases and the C−H···F interactions in 1,3,5-trifluorobenzene, 7, and 1,2,4,5-tetrafluorobenzene, 8, become stronger and more important. Compounds 7 and 8 are
structurally very similar to 1,3,5-triazine and 1,2,4,5-tetrazine, and this similarity further strengthens the argument
that C−H···F interactions resemble C−H···N interactions and provides evidence for their description as weak
hydrogen bonds. 1,2,3,4-Tetrafluorobenzene, 9, is polymorphic but the role of the C−H···F interactions in
the two forms is similar. A comparison of the C−H···F geometries in compounds 1−10 with other C-, H-,
and F-containing compounds in the Cambridge Structural Database reveals that the hydrogen bond properties
are more pronounced in 1−10. It is concluded that only when the carbon acidity is enhanced to the levels of
the compounds in the present study, is the hydrogen-bond nature of the C−H···F interaction even revealed.
This study also demonstrates that the C−F group prefers to form C−H···F interactions rather than F···F contacts.
The behavior of organic fluorine in crystal packing is therefore quite different from the heavier halogens
On difference of properties between organic fluorine hydrogen bond C–H···F–C and conventional hydrogen bond
No full text<p>The existence of C–H···F–C hydrogen bonds in the complexes of trifluoromethane and cyclic molecule (oxirane, cyclobutanone, dioxane, and pyridine) has been experimentally proven by Caminati and co-workers. This study presents a theoretical investigation on these C–H···F–C hydrogen bonds at B97D/6-311++G<sup>**</sup> and MP2/6-311++G<sup>**</sup> levels, in terms of C–H vibrational frequency shifts, atoms in molecules characteristics, and the bonding feature of C–H···F–C hydrogen bonds. It is found that in three important aspects, there are significant differences in properties between C–H···F–C and conventional hydrogen bonds. The C–H···F–C hydrogen bonds show a blueshift in the C–H vibrational frequencies, instead of the X–H normal redshift in X–H···Y conventional hydrogen bonds. The natural bond orbital (NBO) analyses show that σ and <i>p</i> types of lone pair orbitals of the F atom to an antibonding σ<sup>*</sup><sub>H–C</sub> orbital form a dual C–H···F–C hydrogen bond. Such a dual hydrogen bonding leads to the proton acceptor directionality of the C–H···F–C hydrogen bond softer. Our studies also show that the Laplacian of the electron density (▽<sup>2</sup>ρ<sub>BCP</sub>) is not always a good criterion for hydrogen bonds. Therefore, we should not recommend the use of the Laplacian of the electron density as a criterion for C–H···F–C hydrogen bonds.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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