F“ compounds

V-Benzoylation of a 1,2,3,4-tetrahydro derivative is reported, whilst related 1,4-dialkyl derivatives resulted from borohydride reduction of the parent [2,3-f ] compound in the presence of carboxylic acids (79JHC973). 

Few reports of successful 7V-oxide preparation have been found (48JCS1389, 71CR(C)-(273)1529), whilst other papers refer to many failures in attempted A( -oxidations, and the parent [2,3-f ] compound gives the 6-hydroxy derivative instead of an A( -oxide (63JCS5737). 

MiNbC F compounds have a NaC 1-type structure, and are stable only in the case of lithium due to the steric similarity between the lithium ion and Nb3. In the case of other alkali metal cations with larger ionic diameters, the M4Nb04F compounds decompose yielding orthoniobates and simple fluorides of alkali metals, as follows ... 

Structure of Oxy-F Compound F is extremely unstable and is difficult to obtain at a level of purity suitable for NMR studies. However, an oxidation product, Oxy-F, formed when F is left standing at — 20° C, is considerably more stable than F and can be purified to a sufficiently high level of purity. Oxy-F is nonfluorescent and shows absorption maxima at 237 nm and 275 nm (shoulder). The high-resolution FAB mass spectrum indicated the molecular formula of Oxy-F to be C33H3809N4Na2 [m/z 703.2363 (M + Na)+ and 681.2483 (M + H)"1"]. The H and 13C NMR data allowed the assignment of structure 7 to oxy-F (Fig. 3.2.6 Nakamura et al., 1988). 

Unlike the di-f dihalides, such compounds differ little in energy from both the equivalent quantity of metal and trihalide, and from other combinations with a similar distribution of metal-metal and metal-halide bonding. So the reduced halide chemistry of the five elements shows considerable variety, and thermodynamics is ill-equipped to account for it. All four elements form di-iodides with strong metal-metal interaction, Prl2 occurring in five different crystalline forms. Lanthanum yields Lai, and for La, Ce and Pr there are hahdes M2X5 where X=Br or I. The rich variety of the chemistry of these tri-f compounds is greatly increased by the incorporahon of other elements that occupy interstitial positions in the lanthanide metal clusters [3 b, 21, 22]. 

These difficulhes show that the descriphon nearly smooth for the energies of inter-conversion of tri-f compounds is a confession of inadequacy. But other kinds of reaction in which the 4f electrons are conserved suggest that it may be possible to refine nearly smooth into something more precise. To this we now turn. 

The chemical shifts for P—F compounds have been reviewed.The compounds differ from most other organophosphorus compounds because Sp becomes more positive as the electronegativity of the atoms attached to phosphorus increases. The effect is at a maximum for P" compounds. They behave normally with regard to an increase in shielding with increase in co-ordination number and therefore the P" compounds are the least shielded. Thus the largest negative values (— 190 to — 250) are observed for compounds of the type YPFj. With the new value of Sp of + 80 for PFg, the variation of Sp with the number of fluorine atoms in P compounds is now shown to be fairly consistent. The value of Sp has also been reported for a series of aminohalogeno P compounds. -... 

Other major sources of data on the thermochemistry of sulfur-containing compounds are the review by Benson , which is of particular value in evaluating data on radicals and other labile species, and the review of the present author on the thermochemistry of the inorganic S—O—F compounds . 

Specification in Table 9. b Yield of a mixture of 75 and 76 which was separated from the crude reaction product by a silica gel chromatography. All [a]D values were measured in CHC13 at c 1.0.d Optical purity was determined by HPLC on Chiralcel.e Since optically active 75 a and 76 a could not be separated, it is not clear whether both enantiomers are (—)-ones or not. Therefore, both are tentatively shown as (—)-enantiomers. Since [a]D value of each enantiomer is also not clear, [otJD value of the mixture is shown.f Compound is inert to irradiation. Optical purity was not determined. h When an acetone solution of the mixture of (+)— 75c and 76c was kept, racemic 76c crystallized out, mp 135-137 °C. 

Whether bound directly to the silicon or on a carbon bound to the silicon, a fluorine substituent within a silane is highly shielded compared to that in a hydrocarbon. For example, the fluorine of TMS fluoride absorbs more than 25-ppm upfield from that in t-butyl fluoride (Scheme 3.28). (For additional data on Si—F compounds, see Chapter 7, which deals with compounds that have heteroatom-fluorine bonds.)... 

Perhaps not unexpectedly, R3N+F compounds (Scheme 7.3) are deshielded significantly as compared to the R2NF compounds (Scheme 7.4). 

The chloro- or fluorostannanes used were of the type RjXSn-CHRa, where R = bis(trimethylsilyl)methyl or 2,4,6-triisopropylphenyl, R2C is the fluorenylidene moiety and X = Cl or F. Compounds of this type are prepared from R 2SnX2 and LiCHR2. 

Similar MNDOj calculations for N, O, F compounds using bond parameters for O—F and N—F permitted enthalpies of unknown compounds such as FbN(OF)3 to be predicted and possible syntheses evaluated (96). [The input data to this set of calculations included a wrong value for AiJf(F(g)) = 270.3 kJ mol-1. It should be noted that experimental heats of formation of atoms are needed in all these calculations.]... 

The mean bond energy Z (S—F) for SF6 can be regarded as a single bond energy and its transferability to ternary compounds can be examined in S—N—F compounds (see Table XX). 

F Compound R X S. aureus ATCC6538P S. epidermidis 3519 E. coli Juki P. aeruginosa 5007... 

All the N—F compounds involved in the synthesis of a group of C3—C7N-trilluoroalky lam idincs were shock-sensitive explosives in varying degrees. Several were only stable in solution, and others exploded dining analytical combustion. Individually indexed compounds are ... 

F. Compounds Containing Two Bidentate Ligands of the Acetohydroximato(2 ) or Benzohydroximato(2-) Type... 

The lUPAC-authorized italicized prefixal symbol F conveys the sense of perfluoro (e.g., F-alkyl = perfluoroalkyl = Cnp2n+i. By extension, the symbol F- will be used to designate entities (F-chains, F-compounds, F-amphiphiles, F-colloids) that comprise a highly fluorinated moiety or phase. 

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