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The Influence of Fluorine

The commercial popularity of PFCs is primarily due to their unique physical and chemical properties, such as thermal stability, resistance to chemical degradation, repellency to water and oils, and low surface tensions [4]. Many of these properties arise because of the unique properties of fluorine [45]. [Pg.33]

In contrast to the zigzag formation of linear hydrocarbons, long perfluoroalkyl chains are helical, rigid and rod-like structures [49, 52]. This structure, due to the steric repulsion between fluorine atoms, consists of a full helical twist every 13 carbon atoms [49,52]. Short [Pg.33]

As discussed previously, both PFSAs and PFCAs have small acid dissociation constants [1, 4, 5] and are dissociated at environmental pH values. It is important to note that the dissociated and free acid forms of the PFSAs and PFCAs have different physical-chemical properties and environmental partitioning properties. In addition, physical-chemical properties may also differ between various salts of PFSAs and PFCAs, depending on the counter ion present [63]. [Pg.34]


As is consistent with other properties deriving from inductive influences of a substituent, the influence of fluorine substituents on proton... [Pg.39]

The influence of fluorine mixtures with or without reactive gases on the permeability of 02 and N2 through LLDPE was investigated.20 1 It was found, as... [Pg.245]

Figure 10, Schematic of the influence of fluorine to carbon ratio and electrode bias on etching versus polymerization processes in fluorocarbon plasmas, (Reproduced with permission from Ref, 40 J... Figure 10, Schematic of the influence of fluorine to carbon ratio and electrode bias on etching versus polymerization processes in fluorocarbon plasmas, (Reproduced with permission from Ref, 40 J...
Combining the highest electronegativity (4,0) with a rather small polarizability volume which amounts to not more than 0.5 makes fluorine a unique element. Its incorporation into hydrocarbon frameworks results in different electrostatic effects, which are sometimes rarely predictable. However, the influence of fluorine substituents on the acidity of nearby functional groups such as OH, NH,... [Pg.740]

Fig. 12. The template-assisted autocatalyzed peptide replication cycle and the influence of fluorine-fluorine interactions (yellow, template red, electrophilic fragment blue, nucleophilic fragment). (See Colour Plate Section at the end of this book.)... Fig. 12. The template-assisted autocatalyzed peptide replication cycle and the influence of fluorine-fluorine interactions (yellow, template red, electrophilic fragment blue, nucleophilic fragment). (See Colour Plate Section at the end of this book.)...
An interesting paper concerning the influence of fluorine and chlorine substitution on the aromaticity of carbocyclic systems appeared quite recently B. A. Hess and L. J. Schaad, hr. J. Chem. 17, 155 (1978). [Pg.160]

From these arguments it is clear that fluorination has a corresponding effect to diminish the basicity of a compound. For simple carboxylic acids the influence of fluorination on the reduction of basicity falls off dramatically with distance (vide supra).7 6 In gas-phase studies it is apparent that diminution of basicity can be attributed to an increase in the total array of atoms, each of which bears some electron density. Nevertheless, it is clear that when fluorine is attached directly to an anionic center such as that formed by a carboxylic acid its effect is substantially destabilizing.37 40... [Pg.295]

Given that fluorine has a destabilizing influence upon planar carbanions, geometry considerations favor the formation of pyramidal anions.69 71 The influence of /(-fluorination on carbanion stability has been described in a variety of ways. In early work the role of negative hyperconjugation was proposed to account for these effects.72... [Pg.298]

The influence of fluorine substitution on the torsional potential of 1,2-dithioglyoxal has been examined by Toro-Labbd140. However, this study has been carried out at a minimal basis set level, which yields quite poor molecular geometries. This implies that the trends shown for the torsional potentials are only of a qualitative value. The work of Cimiraglia and coworkers141 on variation-perturbation CIPSI calculations of the first excited states of 1,2-dithiete and 1,2-dithiin permits one to rationalize the main features of their electronic absorption spectra. [Pg.1389]

All aspects of the structure, reactivity and chemistry of fluorine-containing, carbon-based free radicals in solution are presented. The influence of fluorine substituents on the structure, the stability and the electronegativity of free radicals is discussed. The methods of generation of fluorinated radicals are summarized. A critical analysis of the reactivities of perfluoro-n-alkyl, branched chain perfluoroalkyl and partially-fluorinated free radicals towards alkene addition, H-atom abstraction, and towards intramolecular rearrangement reactions is presented. Lastly, a summary of the synthetically-useful chemistry of fluorinated radicals is presented. [Pg.97]

The influence of fluorine substituents on the stability of alkyl radicals derives from the same complex interplay of inductive and resonance effects that affects their structure. Simple orbital interaction theory predicts that substituents of the -X type (that is, electronegative substituents bearing lone pairs) should destabilize inductively by virtue of their group electronegativities, and stabilize by resonance to the extent of their ability to delocalize the odd electron. [Pg.102]

As is consistent with other properties deriving from inductive influences of a substituent, the influence of fluorine substituents on proton chemical shifts drops off dramatically as the fluorine becomes farther removed from the hydrogen in question. Thus, protons on the y-carbon or farther away are essentially unaffected by a single F. [Pg.18]

Fig. 18. Schematic diagram for the influences of fluorination upon the n and n bands of C60- (a) The k and n bands of C60. (b) The reduction of the -conjugation leads to the narrowing of the n and it band width by 2a. At the same time, (c) the inductive effect lowers the two bands by b (reproduced by permission of American Chemical Society from J. Phys. Chem. A, 102 (1998) 558 [21]). Fig. 18. Schematic diagram for the influences of fluorination upon the n and n bands of C60- (a) The k and n bands of C60. (b) The reduction of the -conjugation leads to the narrowing of the n and it band width by 2a. At the same time, (c) the inductive effect lowers the two bands by b (reproduced by permission of American Chemical Society from J. Phys. Chem. A, 102 (1998) 558 [21]).
The Influence of Fluorine or Fluorocarbon Groups on some Reaction Centres... [Pg.91]

The Influence of Fluorine or Fluorocarbon Groups on some Reaction Centres Table 4.2 pKa values of some organic acids and alcohols [7]... [Pg.93]

Solvolysis of allylic fluorides may be acid-catalysed [35] and the influence of fluorine substituents at different positions is interesting. Solvolysis of 5.15A occurs where fluorine at the 1-position is able to stabilise an attached carbocation but in the isomer 5.15B fluorine at the 2-position deactivates and solvolysis of 5.15B does not occur under conditions where 5.15A reacts (Figure 5.15). Similar hydrolysis of 1,2-diethoxytetrafluorocyclobutene leads to the well-known, very stable, squarate anion [36] (Figure 5.16a). [Pg.129]

Clearly, attack at the (3-position maximises the influence of fluorine substituents. These same approaches can be used to account for the orientation of substitution in other systems (Figure 9.29). [Pg.314]


See other pages where The Influence of Fluorine is mentioned: [Pg.29]    [Pg.1186]    [Pg.611]    [Pg.703]    [Pg.723]    [Pg.235]    [Pg.339]    [Pg.254]    [Pg.294]    [Pg.1]    [Pg.3]    [Pg.99]    [Pg.373]    [Pg.33]   


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