Fluorine hyperfine splitting

Another example of a hydrated salt which gives the stable radicals obtained from C—C bond breakage is sodium perfluorosuccinate hexa-hydrate. When irradiated at room temperature the principal product is OOC-CFa-CF-COO- (28) but at 77°K. the ESR spectrum of CF2COO is also seen (31). In this case the magnitude of the fluorine hyperfine splitting rules out the electron attachment products such as "OOC-CF2-CF COO2" since /3-fluorine splittings are much smaller. In a detailed study of the 77°K. irradiation products of succinic acid (8) only the radical-ion HOOC-CHjj-CHjj-COOH" was mentioned. More recently it is claimed (16) that some of the weak lines are from HOOC-CH CH2 , but HOOC-CH2 has not been reported. 

Fluorination of aromatics by XeF2 in the presence of HF is thought, contrary to earlier belief, not to involve the aromatic cation radical. However, a cation radical is thought to accept fluoride ion in reactions of XcF2 with easily oxidized aromatics (anisole) in the absence of HF (Anand etal., 1975). In this connection zinc tetraphenylporphyrin has been oxidized to its cation radical with xenon difluoride (Forman et al., 1971) although fluorine hyperfine splitting was found in the esr spectrum, reaction with fluoride ion did not occur. 

TABLE I. An Estimation of the Unpaired Spin Population in Various Orbitals and Their Contributions to the Fluorine Hyperfine Splitting Tensor (in Gauss) of the CF2C00" Radical( ) at 300 K.(a)... 

Alpha - Fluorine Hyperfine Splitting Tensors (Gauss) for Fluorine Containing Radicals in Single Crystals... 

Figure 4. Temperature variation of the a, /3t, and P-2 fluorine hyperfine splittings of the 300°K radical with the magnetic field parallel to a, b, and c. The spectra become too complex to analyze where the curves are shown dashed. From Reference 12.

Table 9. ESR Hyperfine Splitting Constants (a) for Methyl. Fluorinated Methyl, and Fluorinated Alkyl Radicals90 9 100...

Table 1. ESR hyperfine splitting constants for fluorinated methyl radicals [4]...

It is perhaps a pleasant surprise that the X 2 Y 1 state of YbF conforms to a simple case (b) coupling scheme, so that each rotational level N is split by the spin-rotation interaction into states characterised by. 1 = N 1/2 each of these states is further split into a doublet by the fluorine hyperfine interaction, giving final states TV, S, J, /, F) as shown in figure 11.42. The effective Hamiltonian is therefore written in the familiar form (see, for example, our discussion of the CN radical in chapter 9)... 

Replacement by Fluorine. Although such replacement would be informative, because of the large doublet hyperfine splitting to be expected from fluorine, few radicals of this type have been studied. It has been claimed (20) that irradiation of CF4 and SiF4 gives CF3 and SiF3, respectively, which remain trapped in the matrix at 77° or 4°K. The resulting spectra are very complex. 

Pentafluorobenzenesulphonyl fluoride, which may be obtained from the chloride and xenon difluoride,brings about inactivation of the enzyme oc-chymotrypsin, and the kinetics of this process have been studied (other fluorine-containing sulphonyl fluorides were also involved). The e.p.r. spectrum of (inter alia) the radical CsFs SOa, produced from the chloride by abstraction with triethylsilyl radicals, has been reported and the hyperfine splitting constants have been measured at —40 °C, but unambiguous assignments were not possible. Pentafluorophenylsulphonyl... 

The EPR spectrum of NFJ has been measured both as a radiolysis product of NF4 salts and as an intermediate in their formation [1,2, 3]. NFJ salts were y-irradiated [1,2], or mixtures of NF3, F2, and a Lewis acid (e.g., AsFg) were UV-photolyzed at 77 K [1,3]. The spectra proved to be rather complex due to the presence of both nitrogen and fluorine hyperfine structures (hfs) and anisotropies which were different at low and high temperatures [1,2]. Final analysis [5] of a spectrum at 25 K [1] gave the following tensor components of the splitting factor g and hfs constants A(N) and A(F), in MHz, in the respective principal axis system ... 

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