Single Line Perturbation Experiment

Determination of the relative sign of scalar coupling constants, general detection of coupling interaction. The perturbation of a single transition shows intensity changes on related transitions. 

The Selective Population Transfer (SPT) experiment is usually used in spin system analysis with a FT spectrometer. Normally the experimental SPT spectra are compared with calculated SPT spectra simulated using different combinations of coupling constant signs. In common with many textbooks the AMX spin system 2,3-dibromopropionic acid will be used to introduce the concepts behind the SPT experiment. The IH spin system parameters for 2,3-dibromopropionic acid are shown below. The only difference between Spin System A and Spin System B is the sign of the coupling constant J(H(2), H(3)), the results of SPT experiments will be used to distinguish between the two possible spin systems. 

In this particular instance the relative sign of this 3J(H, H) coupling constant does not effect the appearance of the IH spectrum and this is confirmed in Check it 5.2.4.1 where the spectrum for each spin system is simulated. These simulated spectra will also used for comparing the effects of the SPT experiment. In the spin systems ch524.ham and ch524pos.ham the nucleus statement contains three identifiers a, m and x these identifiers are used to label the nuclei. 

In an SPT experiment one spectral line which belongs to a single transition of the spin system is irradiated and the effects on the spectrum observed. To understand the effect of a SPT experiment the energy levels of the spin system must first be calculated. NMR-SIM has the option to generate an energy level scheme of a spin system and to display the results either as a list or in graphical representation. 

Using the calculated energy level list the complete energy level scheme can be deduced as shown in Fig. 5.9. In this figure each energy level is labelled with a number in parenthesis, corresponding to the numbering used by NMR-SIM. Each transition is labelled with a number from 1 to 12 that correlates with a specific spectral line. Thus the 

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The effects of cross correlation can be exploited as a rich source of information on molecular dynamics by measuring relaxation behavior as a single line of a spin multiplet is perturbed. In addition, experiments can be designed to take advantage of the partial cancellation of relaxation effects and thus to obtain narrower lines than might otherwise occur. For example, in two-dimensional NMR it has been possible to utilize the quadratic dependence of CSA on B0 to... 

In a SPT experiment single lines rather than multiplets are perturbed resulting in a higher sensitivity which is particularly beneficial in overcrowded spectra. 

Blinc et a/.177,178 performed 47Ti(/— 5/2) and 49Ti(/= 7/2) quadrupole-perturbed NMR experiments with very high-quality single crystal of BaTiCV The authors observed that in the paraelectric cubic phase T> Tc, the narrow central 1/2) transition lines are surrounded by a broad... 

The apparatus developed by Rees et al. can also be used for single-step FR measurements. In these experiments, the gas phase equilibrium volume, Ve, is only subjected to one half of a square wave perturbation of 1%. Up to 2,048 pressure readings can be recorded by the on-line computer during... 

Applying rf fields of lower intensity to selectively perturb a single resonance or satellite line is the basis of the SPT or selective population transfer experiment. Perhaps the most interesting example of the utilization of SPT experiments, which form the basis for the INEPT, DEPT and other spectral editing experiments that have been developed, is found in the consideration of an AX heteronuclear spin system, e.g. or where the heteronuclear spin is insensitive relative... 

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