Five FLUORINE COMPOUNDS

Figure 15.4 Positive ion ToF SIMS spectra of five fluorinated compounds. Reproduced from Applied Surface Science, Torrisi et al., Copyright 2008 Elsevier...

Five- to six-month-old tobacco plants (Nicotiana tabacum var. Samsun) grown in a glasshouse at 20°C were used for this study. Commercial synthetic substrates employed both for histochemical and biochemical assays were guaiacol, p-phenylenediamine-pyrocatechol (PPD-PC), 3-3 di-aminobenzidine (DAB), tetramethylbenzidine (TMB) and syringaldazine. Isopropylamine and monosodium salts of ferulic acid were also used as substrates as well as their / -fluorinated analogues substituted with a fluorine atom on the / -carbon (Fig. 1). Histochemical observations were done on hand-made transverse sections of fresh tobacco stems. Biochemical assays were performed separately on bark (inner cortical parenchyma, phloem and fibres) and xylem fractions. Technical data of incubation, enzyme extraction, spectrophotometric and electrophoretic assays were given elsewhere (5-7). Synthesis of fluorinated compounds was performed as previously described (4). 

Isomerization reactions of organo-fluorine compounds are included in Houben-Weyl, Vol. 5/3, pp 346-353, where five types of isomerization reactions are covered (1) intramolecular cycli-zation of dienes, (2) opening of cyclobutene rings, (3) opening of cyclobutane rings, (4) isomerization of polyfluorocyclohexadienes, and (5) intramolecular rearrangement of chlorofluoro-and bromofluorocarbons. Much of the work reported is still of fundamental significance and is covered here, where appropriate. Several more later reviews also deal with various aspects of this area.1... 

A bnef paper by Kobayashi indicated some of the potential of this cychzation for making fluorine compounds [5(5] (equation 57) Watanabe et al provided examples of incorporation of a tnfluoromethyl group into a five-membered ring [57] (equation 58) Nevertheless, the full potential of this methodology mpreparing fluorine-containing materials has not been realized... 

Although cyclization to three-membered rings is not as easy and as frequent as are cyclizations to six- and especially five-membered rings, it is not so uncommon with fluorinated compounds. In this particular case, the voluminous carbanion may cyclize easier than would with chlorine substituent for steric reasons. Precedents of such cyclizations are formations of ethylene oxide compounds from fluorohydrins [74]. 

From the F chemical shifts in the NMR spectra of m- and/>-fluoro-phenylcopper were calculated the substituent parameters for copper. The zero value obtained for oj suggests that copper is electronically neutral, but a large or value indicates that copper is capable of a d interaction with the aromatic nucleus 37). The high stability of penta-fluorophenylcopper tetramer relative to many other arylcopper compounds may thus be the result of interactions between the five fluorine atoms and the benzene ring increasing the charge density of the 7r-elec-tron system 37). 

Name the following (a) a compound with two oxygen atoms and one chlorine atom per molecule (b) a compound with one iodine atom and five fluorine atoms per molecule and (c) a compound with one sulfur atom and six fluorine atoms per molecule. 

Interest in such compounds has arisen as a result of the extensive studies being carried out on the stereochemical aspects associated with phosphorus in coordination number five. The observation of distinct axial and equatorial P—F environments for the tetrafluorophosphoranes, by NMR techniques, is possible, whereas this observation is not common to the corresponding hydrocarbon-phosphorus bonded tetrafluorophosphoranes. Further substitution at phosphorus is possible, the tetrafluorophosphoranes and trifluorophosphoranes are reactive compounds, and it is possible to substitute further F atoms for other groups. The experimental techniques described here can be applied to the preparation of other amino fluoro phosphoranes. Further, the same techniques are applicable to other reactions involving phosphorus-fluorine compounds and silicon compounds. 

In dissociative ligand exchange, an equilibrium between four and five coordinate compounds is responsible for the rapid intermolecular fluorine exchange (without racemization at silicon) in compound 196 (p. 163) (321). A similar equilibrium between open and closed forms is also implicated in amino-arylsilanes 213 (p. 174) (133). 

In the case of nitrogen the question is whether five fluorine atoms can be squeezed on to a nitrogen atom. Although calculations predict NF5 to be a potential energy surface minimum, there is enough doubt about the ability of ab initio calculations to accurately handle molecular size (related somewhat to nonbonded interactions [10]) for one to be less than fully confident that this compound will be synthesized. 

Any of a group of five chemically related nonmetallic elements chlorine, bromine, fluorine, iodine, and astatine. Chlorine compounds are used as EP additives in certain lubricating oils, and as constituents of certain petrochemicals (e.g., vinyl chloride, chlorinated waxes). Chlorine and fluorine compounds are also used in some synthetic lubricants. 

Kinetic studies of the gas-phase pyrolysis of 1-aiylethyl acetates (ArCHMe-O COMe Ar = Ph or CeF ) have established that, at 625 K, pentafluoro-styrene is formed 4.60 times more slowly than styrene undo identical conditions. Previous results with monofluoro-compounds show that, if the effects of the fluorine atoms were additive, a retardation factor of 7.75 woidd be obsraved, and it is suggested that the five fluorine atoms are acting to some extent in opposition and that the full —I effect of each cannot be exerted. " Similar conclusions have been reached as a result of studies of the u.v. spectrum of 2,3,4,5,6-pentafluoro-Malachite Green (64) (synthesized via the reaction of pentafluorophenyl-lithium with Michler s ketone), which shows a bathochromic shift of only 37 nm in the A -band with respect to the unfluorinated analogue. ... 

The reactions with fluorinated compounds give, besides the indicated products, the five-nuclear cluster of trivalent ytterbium (Me5C5)ftYb5(p4-F)( i3-F)2(ll-F)s, which is the result of the secondary reaction of (Me5C5)2YbF with the initial R °. 

MISCELLANEOUS FLUORINATED NITROGEN HETEROGYGLIGS Two reviews (1981, 1990) include nitrogen heterocychcs not covered in the present survey (482,483). The 1990 review dealing with four-, five-, and six-membered ring heterocycHc compounds emphasizes biological properties (482). 

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