Spin tickling

In this section we shall outline some of the potential applications of N.M.D.R. to problems in carbohydrate chemistry. A brief discussion will be given of both the spin-decoupling (3, 23) and the spin-tickling (3, 21) methods together with an indication of their respective advantages. Since excellent reviews of the N.M.D.R. method have been published (8, 9) it is only necessary here to mention a few relevant items of nomenclature. 

Data for unsymmetrical compounds are obtained by directly observing the phosphorus AB spectra but the signs of coupling are obtained by spin-tickling or by analysis of higher order spectra. 

Most other homonuclear double-resonance techniques, with names such as spin tickling and selective decoupling, provide information about the arrangement of spin states and the... 

There has been some discussion (127,129,132) of the relative merits of such techniques as pseudo-INDOR, SPT, SPI, spectral analysis, and spin tickling for the determination of the relative signs of coupling constants. It appears to the present writers that much depends upon the particular circumstances, namely, the nature of the spin system (including the relative values of relaxation times), the available instrumentation, and the abilities of the spectroscopist. Certainly, when Tx > "/ A(e g.for C- H ) the effects of simultaneous spin population transfer can make the interpretation of spin tickling effects very tricky. 

In off-resonance decoupling experiments of this type difficulties may arise for certain levels of the decoupling power, since then the combined effects of spin-tickling and spin population transfer may lead to certain important lines having very low intensity. It has therefore been suggested (196) that the amplitude of the irradiating rf field used should... 

An early report (560) mentions the use of homonuclear spin tickling to aid the assignment of the lines of an AB spectrum from an oriented molecule. The method has been applied to the 4-proton spectrum from ethylene oxide in EBBA (561) and to the detection and assignment of weak transitions in the proton spectrum of oriented o-dichlorobenzene. (562)... 

The method of tracing coupling interactions by spin-tickling experiments is based essentially on difference spectra, which are generated either by the subtraction of a SPT spectrum from a unperturbed eontrol spectrum or by the type of pulse sequence used in the SPT experiment. With the latter approach only the signals effected by the SPT experiment appear in the difference spectrum. 

GoviF and Sackmann and Dreeskamp have used spin tickling techniques to determine the magnitude and signs of various coupling constants in olefinic and acetylenic molecules... 

The geminal proton-proton coupling constant in a-chloroacrylo-nitrile is both solvent and temperature dependent.Hetero-nuclear spin tickling experiments were used to show that the sign of the geminal coupling constant is of opposite sign to that of... 

Any pairs of interactions may be separated in this way provided suitable signals are obtainable. To date, such pairs include chemical shift/spin-spin coupling, proton/carbon chemical shifts, as well as dipolar/chemical shifts discussed above. A most promising 2-D plot represents the correlation between proton and carbon shifts. It is also possible to look for polarization transfer only between interacting carbon-proton pairs. This last experiment is otherwise done with fairly complex methods such as spin tickling or off-resonance decoupling, in many cases 2-D NMR can do it in a straightforward manner. Finally, it is possible to detect forbidden transitions by 2-D NMR, but we will not go into it in this book. 

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