Studies of ion-solvent and ion-ion interactions using nuclear magnetic resonance spectroscopy

Chemical shifts of the fluorine nuclear resonance have been measured for fluoride ion in a variety of environments. The shift varies linearly with the mole-fraction of organic solvent and is dependent upon the nature and concentration of added cations and anions. In contrast, the value for the caesium resonance from solutions of caesium salts is independent of the choice of solvent. Large, linear, chemical shifts are observed when other electrolytes are added, the effect being almost entirely due to the anions.     

On the mechanism of the addition of alkoxy radicals to aryl phosphorus compounds

The structure of liquid CS₂ is analysed on the basis of a molecular dynamics experiment involving 512 particles and lasting 24 ps. CS₂ molecules are modelled as rigid entities interacting by a 3CLJ potential. Orientational and statistical mechanical models, so far used for the interpretation of experimental scattering data, are critically examined. The experimentally determined G _d curves are analysed in terms of computer generated g_AB functions. The R-dependent Kirkwood G ⁽²⁾ factor is studied carefully. It is shown that G _∞ ⁽²⁾ is not a measure of nearest neighbourhood correlations. g_AB functions, at most, being extractable from the experimental data, a simple superposition ansatz relating g_AB and g _l00 functions is tested.     

Measurement of17O quadrupole interactions and identification of the diamagnetic fraction in ice by muon level crossing resonance

By means of Level Crossing Resonance in a sample of ice which is enriched in H₂ ¹⁷O, the final diamagnetic state of implanted positive muons is determined to be the muonium-substituted molecule HMuO, accommodated in the regular and fully relaxed Ih structure. The¹⁷O quadrupole coupling constant is measured to be 6.1 MHz at 200 K assuming an asymmetry parameter close to unity, a decrease of about 5% relative to that in normal ice Ih at 77 K. The isotope effect is attributed to a greater polarization in the vicinity of a muonium (as opposed to a normal hydrogen) bond. At 50 K, an additional resonance is observed which could correspond to a precursor state, so far not definitely identified. One possibility is a muon trapped at a Bjerrum L-defect, giving a {H₂O−Mu−OH₂}⁺ species with an,¹⁷O quadrupole coupling constant of 8.2 MHz and asymmetry parameter of 0.55. Above this temperature, the fall in the (Gaussian) line-width parameter is attributed to the increasing rate of proton or muon migration, the correlation time dropping from 4 μs at 80 K to 1 μs near the melting-point. The increase in the diamagnetic fraction with rise in temperature is attributed to the increasing proportion of trapping sites available for muon capture.     

A paramagnetic silver-cyanomethane derivative

The e.s.r. spectrum of a silver(0)cyanomethane complex is described, the structure of which resembles that of an imino radical.     

Reply to comment by J.T. Wang and F. Williams on the stability of alkyl halide and related σ* anions

Conditions under which σ^* anions (R^.-hal)^? are likely to be stable with respect to dissociation into R^. + hal^? are discussed. It is pointed out that if dissociation leads to

+ hal^., then an important factor is the shape of

rather than that of R^..     

pp Homoconjugation in organic radicals

ESR data for various radicals of type R₂?CR₂X, when R is H or alkyl, and X is either Cl, Br or I, or PR₂ and AsR₂, are discussed in terms of pp homoconjugation. For the β-halogen radicals, the small size of the anisotropic coupling provides some evidence for this effect, but for the β-PR₂ and β-AsR₂ radicals, the greatly enhanced isotropic coupling to ³¹P or ⁷⁵As compared with those for the corresponding cation-radicals, R₂?CR₂PR⁺₃ or R₂?CR₂AsR⁺₃, is taken as good evidence for homoconjugation.     

An ESR study of electron loss and electron capture by silver (I) ions in methyl cyanide

Exposure of solutions of silver (I) perchlorate in methyl cyanide to ⁶⁰Co γ-rays at 77 K gave Ag(II) and Ag(O) centres in addition to radicals formed from the solvent. Their ESR spectra showed hyperfine features from ¹⁰⁹Ag and ¹⁰⁷Ag together with features from four equivalent ¹⁴N nuclei. The results are contrasted with those previously reported for solutions of silver (I) nitrate in methyl cyanide, which gave Ag(II) and Ag(O) centres whose ESR spectra were devoid of any ¹⁴N hyperfine features.