Isotropic line

Equation 10.2 affords a single, isotropic line split into a triplet by the 14N nucleus and a further splitting into doublets by the II nucleus, altogether resulting in a pattern of six-lines of equal width and intensity. For particular magnitudes of AN and AH the lines may partly, or completely overlap as is the case for the HO adduct of DMPO, which has AN AH, resulting in a four-line pattern with 1 2 2 1 intensities (Figure 10.2). 

Fig.2 Solid-state P H MAS-NMR spectrum of l[Brj. The asterisk and cross denote the isotropic lines attributable to the two- and four-coordinate phosphorus atoms, respectively (according to [37])...

Schindler W, Sharko PT, Jonas J. Raman study of pressure effects on frequencies and isotropic line shapes in liquid acetone. J Chem Phys 1982 76 3493-3504. 

Fast and ultra-fast spinning are able to remove all spinning sidebands and simplify the analysis of spectra leaving only the isotropic lines. However, in some cases static or slow sample spinning spectra are required since their inspection... 

Another problem, which very often complicates the analysis of 31P spectra, is overlapping of the isotropic lines. Ironside et al.45 while investigating a mixture of hydroxyapatite, Ca10(PO4)6(OPI)2 and sodium dihydrogen phosphate,... 

EPR spectroscopy provides insight into the structural rearrangement associated with this transformation. The EPR spectrum of the V0HP04-O.5H2O precursor consists of an isotropic line, which is narrowed as a consequence of effective spin-spin exchange interactions within the face-sharing dimers of the struc-... 

Figure 9J8. Observed and simulated MAS NMR spectra of PbSiOs and the high-temperature form of Pb2Si04. Note the complex sideband patterns arising from the 3 Pb sites in PbSi03 and the 4 inequivalent Pb atoms in Pb2Si04- The isotropic lines are denoted by asterisks. From Fayon et al. (1997), by permission of the American Chemical Society.

The development of new ID and 2D pulse sequences enables the spectroscopist to obtain structure and dynamic information about systems that were previously very hard to study. As an example is reported in Fig. 3.2.13 the 2D spectrum of erythromycin A measured with the FIREMAT (Five p Replicated Magic Angle Turning ) technique [30]. The slow spinning speed of 390 Hz produces a spinning sideband pattern for each peak in one dimension, whereas a multipulse sequence in combination with a special processing method produces isotropic lines in the second dimension. 

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