Halogens fluorine atom

PTFE containing halogen (fluorine) atoms, is an effective flame retardant by itself for PC and ABS. 

Numerous ionic compounds with halogens are known but a noble gas configuration can also be achieved by the formation of a covalent bond, for example in halogen molecules, X2, and hydrogen halides, HX. When the fluorine atom acquires one additional electron the second quantum level is completed, and further gain of electrons is not energetically possible under normal circumstances, i.e... 

The nonbonding electron clouds of the attached fluorine atoms tend to repel the oncoming fluorine molecules as they approach the carbon skeleton. This reduces the number of effective coUisions, making it possible to increase the total number of coUisions and stiU not accelerate the reaction rate as the reaction proceeds toward completion. This protective sheath of fluorine atoms provides the inertness of Teflon and other fluorocarbons. It also explains the fact that greater success in direct fluorination processes has been reported when the hydrocarbon to be fluorinated had already been partiaUy fluorinated by some other process or was prechlorinated, ie, the protective sheath of halogens reduced the number of reactive coUisions and aUowed reactions to occur without excessive cleavage of carbon—carbon bonds or mnaway exothermic processes. 

If the competition data are compared with electronegativity values for the halogens 85>, then tetrafluorobenzyne is clearly in an anomalous position. The only reasonable explanation available at present is that tetrafluorobenzyne is so destabilized by the inductive effect of the fluorine atoms that it has lost a considerable amount of the selectivity which arynes normally show. Estimates for the heats of formation of the isomeric dichlorobenzynes and for tetrachlorobenzyne have recently been made from mass spectrometric studies and these do indicate a low stability for tetrachlorobenzyne 86>. Evidently more data are required for the tetrahalogenobenzynes. 

For the formation of indoles 2 and 3 we assumed that amines 1 first reacted with fBuLi at -110°C to give N-(2-lithioallyl)amines 4, through halogen-metal exchange 23 this was confirmed by deuteration and isolation of the deuteriated amine 5 a (Scheme 2). Intermediate 4, which is stable for several hours at —110 °C, probably undergoes proton-abstraction ortho to the fluorine atom by the additional equivalents of fBuLi when the temperature is raised to — 40 °C giving the intermediate 6. The subsequent elimination of LiF produces a benzyne intermediate 7, which is efficiently... 

An alkyl halide (also known as a haloalkane) is an alkane in which one or more hydrogen atoms have been replaced with halogen atoms, such as F, Cl, Br, or I. The functional group of alkyl halides is R—X, where X represents a halogen atom. Alkyl halides are similar in structure, polarity, and reactivity to alcohols. To name an alkyl halide, first name the parent hydrocarbon. Then use the prefix fluoro-, chloro-, bromo-, or iodo-, with a position number, to indicate the presence of a fluorine atom, chlorine atom, bromine atom, or iodine atom. The following Sample Problem shows how to name an alkyl halide. 

Fluorine does not occur in a free state in nature, and because fluorine is one of the most reactive elements, no chemical can free it from any of its many compounds. The reason for this is that fluorine atoms are the smallest of the halogens, meaning the electron donated by a metal (or some nonmetals) are closer to fluorines nucleus and thus exert a great force between the fluorine nuclei and the elements giving up one electron. The positive nuclei of fluorine have a strong tendency to gain electrons to complete the outer shell, which makes it a strong oxidizer. 

Since the size of halogen atom Increases as we go down the group in the periodic table, fluorine atom is the smallest and iodine atom, the largest. Consequently the carbon-halogen bond length also Increases from C—to C— I. Some typical bond lengths, bond enthalpies and dipole moments are given in Table 10.2. 

When bonded to an unsaturated carbon atom or to an arene, the fluorine atom exerts an inductive electron-withdrawing effect (cti>0) and an electron-donating effect through resonance (ctr < 0), both being very superior to the effects of the other halogens (Figure 1.1). The values of the Hammet parameters crj and fluorinated substituents are reported in Table 1.13. " ... 

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