Solvents for solution studies

Samples for solution NMR spectroscopy are generally prepared using deuterated solvents. One reason for this is that, were non-deuterated solvents to be used (e.g. CH3CI in place of CD3CI) for a H NMR spectroscopic experiment, the signals due to the solvent would swamp those due to the sample. Deuterated solvents are commercially available, typically with 99.5% H label incorporated. The remaining unlabelled compound provides a useful internal reference signal in the H NMR spectrum of the sample under study. 

The presence of a paramagnetic centre (i.e. a craitre with one or more unpaired electrons) in a compotmd has significant consequences on the H NMR spectrum of the compound. Firstly, the local magnetic field at each nucleus is affected. The energy 

An example of a paramagnetic centre is a Co ion which, in an octahedral complex, has one or three unpaired electrons (see Chapter 20). The figure below shows the H NMR spectrum of the Co complex [Co(phen)3] (phen = 1,10-phenanthro-line), the structure of which is shown below. There are four different aromatic proton environments in the complex, and the chemical shifts of the signals assigned to these H nuclei fall in the range 6 - -110 to +15ppm. 

In some cases, signals may be broadened and this can affect the measurement of the relative integrals of signals. For example, signals arising from protons attached to N are broadened due to quadrupolar relaxation by N (/ = 1). Exchange with solvent protons also causes broadening, e.g.  

---