New techniques in Fourier transform nuclear magnetic resonance
New techniques in Fourier transform nuclear magnetic resonance spectroscopy are introduced with chemical applications to the study of molecules in the liquid state. Recently a theoretical description of magnetic resonance in terms of single transition operators has been introduced which provides a g...
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University of Oxford
1982
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| Online Access: | http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.331154 |
| Summary: | New techniques in Fourier transform nuclear magnetic resonance spectroscopy are introduced with chemical applications to the study of molecules in the liquid state. Recently a theoretical description of magnetic resonance in terms of single transition operators has been introduced which provides a geometric interpretation of the behaviour of a spin system. This formalism is developed further and extended to the general description of a system of nonequivalent spin-1/2 nuclei. Operator combinations are introduced which allow extension of the convenient geometric representation to the concerted behaviour of coupled spins. The operator formalism is applied to the excitation and detection of multiple quantum transitions, providing a description of the processes in terms of rotating vectors. The process of coherence transfer in two-dimensional Fourier transform experiments is studied in detail and single transition operators are used to derive a general expression for the tip angle dependence of the detection process. A method of discriminating the sense of precession of double quantum coherence is presented and applied to the correlation of chemical shifts of carbon-13 spins in natural abundance. A new technique is presented for the correlation of chemical shift information in coupled proton spin systems in which excitation and indirect detection of double quantum transitions is used to assign coupling patterns in complex spectra. The tip angle dependence of the detection process is used to suppress all but direct correlation of spins. Methods for the measurement of heteronuclear coupling constants in proton spectra are introduced which discriminate the heteronuclear satellites from the parent proton resonance. The technique provides a sensitivity advantage over direct measurement of coupling in the heteronuclear spectrum. Ambiguities are encountered when the protonproton and proton-heteronuclear coupling constants are of the same order of magnitude. This problem is overcome by extension of the basic experiment to its two-dimensional analogue. |
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