Chapter 7 Multiple Choice Questions

. The nuclear spin Hamiltonian includes components Ĥ_ext and Ĥ_int, where

Ĥ_ext describes the interaction with the spectrometer magnetic field B₀, while Ĥ_int describes the interactions between spins.

Ĥ_ext describes the interaction of the spins with the pulses B₁ used to excite the nuclear spins. Ĥ_int describes the interaction of the spins with the spectrometer magnetic field B₀.

Ĥ_ext describes the interaction of the spins with the spectrometer magnetic field B₀ and with the pulses B₁ used to excite the nuclear spins. Ĥ_int describes the interaction between spins.

Ĥ_ext describes the interaction of the spins with the spectrometer magnetic field B₁, while Ĥ_int describes the interaction with the pulses B₁ used to excite the nuclear spins.

. Anisotropic components of Ĥ_int, i.e., those that depend on the orientation of the individual molecule with respect to the spectrometer magnetic field B₀, are due to

chemical shift, dipolar and quadrupolar interactions.

chemical shift, scalar coupling and spin rotation.

spin rotation, scalar coupling and quadrupolar interactions.

chemical shift and scalar coupling.

. Solid-state NMR spectra measured without magic angle spinning

give results identical to those measured with magic angle spinning.

can be measured but the resulting spectra will differ from those measured with magic angle spinning.

can only be obtained for spin ½ nuclei, and the results will differ from those measured with magic angle spinning.

cannot be measured.

. Magic angle spinning

averages to zero the contribution of chemical shift anisotropy, reduces both dipolar and some quadrupolar interactions, making the resonances in solid-state spectra sharper.

averages to zero the contribution of chemical shift anisotropy, making resonances in solid-state spectra broader.

averages to zero the contribution of chemical shift anisotropy and reduces both dipolar and quadrupolar interactions, making resonances in solid-state spectra broader.

does not impact on the overall appearance of the solid-state spectra.

. Spinning the sample more slowly than the width of the static lineshape of the signal in Hz

results in a sharper resonance at the isotropic chemical shift due to removal of spinning sidebands.

results in a broader resonance at the isotropic chemical shift accompanied by spinning sidebands.

results in a sharper resonance at the anisotropic chemical shift and the presence of the spinning sidebands.

does not have any effect on the linewidth of the resonance.

. One of the ways to remove dipolar interactions from solid-state ¹H NMR spectra is to

combine fast magic angle spinning, isotopic dilution and use a very high magnetic field spectrometer.

use fast magic angle spinning and a very low magnetic field spectrometer.

combine isotropic dilution with a very high magnetic field spectrometer and record spectra without magic angle spinning.

combine slow magic angle spinning, isotopic dilution and use a very low magnetic field spectrometer.

. Hartmann-Hahn matching is the basis of cross-polarisation and allows

polarisation transfer via the quadrupolar interaction between more sensitive spins I and a less sensitive spin S aimed to improve the sensitivity of measurements of spin S.

polarisation transfer via the dipolar coupling between a more sensitive spin S and a less sensitive spin I to improve the sensitivity in measurements of spin S.

polarisation transfer via the dipolar coupling between a more sensitive spin I and a less sensitive spin S to improve the sensitivity in measurements of spin I.

polarisation transfer via the dipolar coupling between a more sensitive spin I and a less sensitive spin S to improve the sensitivity in measurements of spin S.

. The most commonly used spin I in cross-polarisation experiments is

¹H due to its high natural abundance and large gyromagnetic ratio.

¹⁵N due to its low natural abundance and small gyromagnetic ratio.

¹³C due to its low natural abundance and small gyromagnetic ratio.

³¹P due to its high natural abundance and large gyromagnetic ratio.

. Cross-polarisation build-up curves can be used to

probe distances between and the mobility of spins due to the dependence of cross-polarisation build-up on spin mobility.

probe distances between and mobility of spins due to the dependence of cross-polarisation build-up on spin relaxation.

probe distances between and mobility of spins since spin relaxation is independent of spin mobility.

probe distances between and mobility of spins due to a dependence of spin relaxation on spin mobility and separation.

. Incomplete averaging of quadrupolar interactions during magic angle spinning

can provide useful information about the structure and mobility by analysis of the isotropic chemical shift.

can provide useful information about structure and mobility through analysis of the quadrupolar lineshape.

can provide useful information about structure through analysis of the chemical shift anisotropy.

does not provide any information beyond line broadening.

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