Line broadening solvent effect

The aqua ion is not easily reduced nor oxidized. It is the slowest reacting of the bivalent transition metal ions with e " k = 7.7 X 10 M s ) and the product Mn+q is very reactive. However Mn(CNR)5 (R = a variety of alkyl and aryl groups) is stable and the selfexchange in the Mn(l,ll) hexakis(isocyanide) system has been studied by Mn and H nmr line broadening. The effects of solvent, temperature, pressure and ligand have been thoroughly explored. 

It is quite common to observe that the lines in a nitroxide spectrum show variations in width. One feature which contributes to this is the anisotropy of the nitroxide grouping, as a consequence of which the high field component of the nitrogen triplet may be perceptibly broadened. This effect is particularly noticeable when free tumbling of the nitroxide molecule is restricted either by the viscosity of the solvent or when the radical is incorporated into a very large (e.g. polymer) molecule. This selective line broadening is, of course, one of the principal sources of information in spin-labelling experiments (Berliner, 1976). 

Esr line broadening. When one of the couples if uncharged, the electrostatic work term is approximately zero. Structural differences between the two species are also likely to be small (X small). The effect of solvent is contained in Using Eqns. (5.23) and (5.25)-(5.27), a plot of log A .xch vs (Dop -ZJ " ) should be linear with negative slope. 

Due, in the main, to quadrupolar line-broadening effects, together with the poor sensitivity, there has been relatively little general interest in 14N magnetic resonance studies and, although the quadrupolar broadening has been shown to be minimized by the use of low viscosity solvents,465 the 14N chemical shifts of only four pyrroles have been reported.465,466 The 14N chemical shift of pyrrole has been reported as either 230465 or 227466 ppm relative to the N02 ion 14N resonance, and values of 227, 230, and 225 ppm have been recorded for 1-methylpyrrole, 2,5-dimethylpyrrole, and l-methyl-2-methoxy-carbonylpyrrole, respectively.465 The associated effect of electric... 

The concentration of the sample in a particular solvent has little effect on chemical-shift values and, because of the inherently low sensitivity of 13C-n.m.r. spectroscopy, it is advantageous to use as concentrated solutions as possible when measuring these spectra. However, increased concentration, and consequently increased viscosity, causes line broadening due to decreased, spin-lattice relaxation-times (Tj values),18 and thus, poorer resolution. Certain solvents that tend to give viscous solutions (for example, Me2SO-d6) may also give decreased resolution. 

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