Multipulse NMR

Phase cycling is widely employed in multipulse NMR experiments. It is also required in quadrature detection. Phase cycling is used to prevent the introduction of constant voltage generated by the electronics into the signal of the sample, to suppress artifact peaks, to correct pulse imperfections, and to select particular responses in 2D or multiple-quantum spectra. 

Since the advent of multipulse-NMR techniques, more detailed 1H-NMR studies on methylcyclo-hexanes547, phenylcyclohexanes548, neomenthyl halides549 and bicydo[4.4.0]decanes 550 551 have been undertaken. The two diastereomeric 4-fm-butyl-7,ll-diphenylspiro[5.5]undecane-1,9-diones (3) and (4) could be identified unambiguously552, and substituted spirodioxane cyclohexanes such as, 9- m-butyl-2-methyl-1.3-dioxaspiro[5.5]undecane (5), have also been investigated553,554. 

R. Freeman Spin Choreography Basic Steps in High Resolution NMR , Oxford University Press, Oxford, 1998. An excellent text covering multipulse NMR spectroscopy. 

Modem multipulse NMR experiments are critically dependent on the application of rf pulses of known duration (the pulse width) that correspond to precise magnetisation tip angles, most frequently 90° and 180°. Pulse width calibrations are normally defined for the 90° pulse (PW90), from which all other... 

Even one-dimensional (ID) NMR spectra are often adequate to deduce some delicate configurational and conformational characteristics of a molecule. Such features are inferred from the chemical shifts and coupling constants of the respective protons as well as from the position of the easily detectable singlets of the C18 and C19 angular methyl groups. The use of the nuclear Overhauser effect (NOE) and various multipulse NMR techniques enable the solving of even more difficult problems. 

Kup Kupce, E., Lukevics, E. Multinuclear and Multipulse NMR of Organosilicon Compounds, in Isot. Phys. Biomed. Sci., Vol. 2 (Isot. Appl. NMR Stud.), Buncel, E., Jones, J. R. (eds.), Elsevier, Amsterdam, p. 213, 1991. 

M. Robin BendaU, R.E. Gordon, Depth and refocusing pulses designed for multipulse NMR rvith surface coils, J. Magn. Reson. 53 (1983) (1969) 365—385. 

NMR Spectra of fiuoropolymers provide abundant structural information from the many NMR interactions presented in these systems. For the many possibilities of performing multidimensional/multipulse/multiple-resonance NMR experiments, we have only presented here the tip of the iceberg. Taking care of all the spin interactions to properly implement multipulse NMR techniques can be extremely challenging yet very necessary. The need for the information provided from advanced NMR experiments makes the efforts worthwhile. 

Turner C J 1984 Multipulse NMR in liquids. Prog Nuc Magn Res Spec 16 311-370... 

Figure 14 Schematic illustration of relaxation measurement and behavior of magnetization in response to multipulse NMR experiments (a) 7 measurement and (b) T2 measurement. Reproduced with permission from Rinaldi, P. L. Monwar, M. Encyclopediaof Spectroscopy and Spectrometry, 2nd ed. Elsevier, Oxford, UK, 2010, Copyright 2010 Elsevier. ...

Many multipulse NMR experiments are based on coherence selection, where it is desirable to detect only one of two or more signal components, and the remaining signal components must be eliminated from the spectrum. Examples of this are H C heteronudear correlation experiments such as HSQC, HMQC, HMBC, and H2BC (Table 4), where it is desirable to detect 1% of the proton signal from coupled to... 

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