31P hyperfine couplings

Only the isotropic 19F and 31P hyperfine coupling constants were obtained and hence it is difficult to draw any firm conclusions about the structure of this 7r-radical. The parameters are quite similar to those for NF2 except if one assumes that, as with NF2, the spin-density is almost 100% on the central atom, the U-value for 31P is lower than that for 14N. This probably means that the bond angle for PF2 is less than that for NF2. 

When several magnetically equivalent nuclei are present in a radical, some of the multiplet lines appear at exactly the same field position, i.e., are degenerate , resulting in variations in component intensity. Equivalent spin-1/2 nuclei such as 1H, 19F, or 31P result in multiplets with intensities given by binomial coefficients (1 1 for one nucleus, 1 2 1 for two, 1 3 3 1 for three, 1 4 6 4 1 for four, etc.). One of the first aromatic organic radical anions studied by ESR spectroscopy was the naphthalene anion radical,1 the spectrum of which is shown in Figure 2.2. The spectrum consists of 25 lines, a quintet of quintets as expected for hyperfine coupling to two sets of four equivalent protons. 

P contact shifts in ligands coordinating through P-O moieties in oxovana-dium(IV), cobalt(II) and nickel(II) complexes are downfield and of the order of 103 ppm [69-71]. Smaller downfield shifts are observed for nickel-coordinated P-S moieties [72]. Direct P-M coordination gives rise to even larger hyperfine coupling than in P-O moieties. In low spin cobalt(H) complexes A/h values of the order of 102 MHz are found [73]. 

RADIATION CHEMISTRY H Table VI. Magnetic Parameters 14N, 15N, 31P, or 33S Hyperfine Coupling constants (gauss) ... 

Perhaps the most important conclusion to be drawn from results for metal atoms in groups such as 7SiL3 or -PL3+ is undetectably small (70,71). Indeed, the R2C- moiety displays hyperfine interaction with H and 13C that suggest normal planarity at carbon with essentially unit spin-density thereon, and coupling to the metal atom (specifically, 31P) is small and probably negative. This implies that spin-density is acquired by spin-polarisation of the C-M o-electrons and not by p -d delocalisation, as is so often... 

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