Electronegativity of fluorine

The oxides of fluorine are more correctly called oxygen fluorides because of the greater electronegativity of fluorine. 

Carbon-fluorine bonds are quite strong (slightly stronger than C—H bonds) and like polyethylene Teflon is a very stable inert material We are all familiar with the most characteristic property of Teflon its nonstick surface This can be understood by com paring Teflon and polyethylene The high electronegativity of fluorine makes C—P bonds less polarizable than C—H bonds causing the dispersion forces m Teflon to be less than those m polyethylene Thus the surface of Teflon is even less sticky than the already slick surface of polyethylene... 

Substitution of fluorine for hydrogen in an organic compound has a profound influence on the compound s chemical and physical properties. Several factors that are characteristic of fluorine and that underHe the observed effects are the large electronegativity of fluorine, its small size, the low degree of polarizabiHty of the carbon—fluorine bond and the weak intermolecular forces. These effects are illustrated by the comparisons of properties of fluorocarbons to chlorocarbons and hydrocarbons in Tables 1 and 2. 

Nucleophilic Reactions. The strong electronegativity of fluorine results in the facile reaction of perfluoroepoxides with nucleophiles. These reactions comprise the majority of the reported reactions of this class of compounds. Nucleophilic attack on the epoxide ring takes place at the more highly substituted carbon atom to give ring-opened products. Fluorinated alkoxides are intermediates in these reactions and are in equiUbrium with fluoride ion and a perfluorocarbonyl compound. The process is illustrated by the reaction of methanol and HFPO to form methyl 2,3,3,3-tetrafluoro-2-methoxypropanoate (eq. 4). 

Phenyllithium caimot be formed from fluoroben2ene. Instead, the electronegativity of fluorine makes the ortho hydrogen sufficiently acidic to permit reaction with / -butyUithium in tetrahydrofuran at —50°C to give 2-fluorophenyllithium [348-53-8]. An isomer, 4-fluoropheny11ithium [1493-23-8] was reported to be explosive in the soHd state (167). 

The incorporation of fluoride in place of hydroxyl groups is chemically straightforward [59,60] and, as we have seen, results in a substance of greater resistance to acid attack. This is partly due to the greater electronegativity of fluorine, which means that the electrostatic attraction between Ca + and F is greater than that between Ca + and OH. As a result, the fluoridated apatite lattice is more stable than hydroxyapatite [61-63]. It is also more crystalline [64]. 

Even the F for Cl change transmuting CeHsCCl into CeHsCF is accompanied by a diminution in reactivity CeHsCF reacts about one-half as rapidly as CeHsCCl with the alkenes of Table 7.5. This lowering of reactivity can be attributed to greater stabilization of CeHsCX when X=F, as opposed to X=C1. Fluorine is a better resonance electron donor to the vacant carbene 2p orbital than chlorine, and this factor (rather than the greater electronegativity of fluorine) appears to be dominant. ... 

In the case of insertion toward fluorine (41), there is an even greater amount of positive-positive charge repulsion between the ortho and ipso carbons than in the transition state and this effect is responsible, in part, for a higher activation barrier for insertion toward F to form 41 than away from fluorine to form 40. Therefore, the origin of the pronounced influence of ortho,ortho-difluoro substitution on the lifetime of singlet arylnitrene and the increased activation energy of its cyclization is the result of combination of the steric effect and the extraordinary electronegativity of fluorine atom. 

High electronegativity of fluorine—> Polar or ionic C—F bonding... 

It is interesting that in general fluorine atoms attached to carbon do not have significant power to act as proton acceptors in the formation of hydrogen bonds46 in the way that would be anticipated from the large difference in electronegativity of fluorine and carbon. 

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