Chapter 5 Multiple Choice Questions

. The INEPT experiment

increases the intensity of signals from insensitive nuclei by polarisation transfer from more sensitive nuclei; it is only possible when both spins have positive gyromagnetic ratio.

increases the intensity of signals from insensitive nuclei by polarisation transfer from more sensitive nuclei; it is only possible when both spins have negative gyromagnetic ratio.

increases the intensity of NMR signals from insensitive spins due to polarisation transfer from a more sensitive spin; the enhancement is equal to the ratio of gyromagnetic ratios of the two spins involved.

decreases the intensity of signals from insensitive nuclei due to polarisation transfer from more sensitive nuclei; the reduction in intensity is equal to the ratio of gyromagnetic ratios of the two spins involved.

. 2D NMR experiments generate a map with cross-peaks relating two NMR properties encoded in the magnetisation (F2 and F1).

Dimension F2 is the real-time dimension containing the 1D NMR FID signal, while dimension F1 is a synthesized time dimension produced by incrementing a delay in the pulse sequence and encoding the NMR property of interest.

Dimension F1 is the real-time dimension containing the 1D NMR FID signal, while dimension F2 is a synthesized time dimension produced by incrementing a delay in the pulse sequence and encoding the NMR property of interest.

Dimension F2 is the real-time dimension containing a 2D NMR FID signal, while dimension F1 is a synthesized time dimension produced by incrementing the pulse lengths in the pulse sequence and encoding the NMR property of interest.

Dimension F2 is the real-time dimension containing a 1D NMR FID signal, while dimension F1 is the synthesized time dimension produced by incrementing the pulse lengths in the pulse sequence and encoding the NMR property of interest.

. A 2D NMR experiment which encodes homonuclear scalar couplings is a

COSY experiment, and is practicable between any spins, including those at low natural abundance, e.g., ¹³C/¹³C, ²H/²H.

COSY experiment, and is practicable between abundant or enriched spins, e.g., ¹H/¹H, ³¹P/³¹P.

NOESY experiment, and is possible between abundant spins, e.g., ¹H/¹H, ³¹P/³¹P.

HOESY experiment, and is possible between abundant spins, e.g., ¹H/³¹P, ³¹P/ ¹H.

. An advantage of inverse 2D NMR experiments (HSQC, HMQC and HMBC) in inorganic systems is

a significant gain in sensitivity for spins of very low gyromagnetic ratio, e.g., ⁵⁹Fe, ⁸⁹Y ¹⁰³Rh and ¹⁸³W when detected via an abundant spin of higher gyromagnetic ratio, e.g., ¹H or ³¹P.

a significant gain in sensitivity for moderately abundant spins, e.g., ¹²⁹Xe, ²⁰⁷Pb and ¹⁹⁵Pt when detected via an abundant spin of lower gyromagnetic ratio, e.g., ¹⁰³Rh, or ¹⁰⁹Ag.

a significant gain in sensitivity for spins of low abundance such as ¹¹³Cd and ¹¹⁹Sn when detected via a more abundant spin of similar gyromagnetic ratio, e.g., ³¹P.

a significant gain in sensitivity for spins of high gyromagnetic ratio, e.g., ¹H, or ¹⁹F, when detected via a less abundant spin of high gyromagnetic ratio, e.g., ²⁰⁵Tl.

. When comparing HMQC and HSQC experiments

HSQC is a shorter pulse sequence than HMQC so is less prone to signal losses due to pulse imperfections and relaxation, whereas HMQC provides higher resolution and is less subject to the emergence of the passive couplings between the sensitive spins.

HMQC is a shorter pulse sequence than HSQC so is less prone to signal losses due to pulse imperfections and relaxation, whereas HSQC provides higher resolution and passive couplings between the sensitive spins are not seen.

HMQC is a shorter pulse sequence than HSQC and is more prone to signal losses due to pulse imperfections and relaxation. HMQC also provides higher resolution and passive couplings between the sensitive spins are not seen.

HSQC is a shorter pulse sequence than HMQC so is less prone to signal losses due to pulse imperfections and relaxation. Both HMQC and HSQC provide similar resolution.

. The HMBC sequence is

routinely used to observe long-range H-H couplings and suffers from inherently low sensitivity due to loss of signal as a result of relaxation during the delay used to remove large short-range couplings.

routinely used to observe short-range H-X couplings and suffers from inherently low sensitivity due to loss of signal through relaxation during the delay used to remove small short-range couplings.

routinely used to observe long-range H-X couplings and suffers from inherently low sensitivity due to loss of signal through relaxation during the delay used to remove large short-range couplings.

routinely used to observe short-range H-X couplings and is characterized by excellent sensitivity and resolution.

. The 2D NMR NOESY experiment is used to

identify spins that are bonded covalently and relax through the dipolar relation mechanism. NOESY frequently contains artefacts due to COSY and HSQC.

identify spins that are located close to each other in space and relax through any type of mechanism. NOESY frequently contains artefacts due to COSY and EXSY.

identify spins that relax through the dipolar relation mechanism and are separated by more than 5Å in space. NOESY frequently contains artefacts due to COSY and EXSY.

identify spins that relax through the dipolar relation mechanism and are located close to each other in space. NOESY frequently contains artefacts due to COSY and EXSY.

. HOESY is

a variation of NOESY for the correlation of heteronuclear, abundant spins through space, e.g. ¹H and ¹⁹F.

a variation of NOESY for the correlation of homonuclear, abundant spins through space, e.g. ¹H.

a variation of NOESY for the correlation of heteronuclear spins through space, where only one of the spins is abundant, e.g., ¹H or ¹⁹F, while the second spin is not abundant, e.g. ¹³C or ¹⁵N.

a variation of NOESY for the correlation of heteronuclear spins through space, where both spins can be either abundant or not.

. Hyperpolarisation is a procedure to

improve the sensitivity of NMR measurements and is particularly valuable for sensitive spins, e.g. ¹H and ¹⁹F.

improve the sensitivity of NMR measurements and is particularly valuable for insensitive spins, e.g. ¹⁷O and ¹²⁹Xe.

improve both the sensitivity and resolution of NMR measurements and is particularly valuable for more sensitive spins, e.g. ¹H and ²⁷Al.

improve the resolution of NMR measurements and is particularly valuable for sensitive spins, e.g. ¹H and ¹⁹F.

. SABRE when compared to traditional PHIP experiment

is a hyperpolarisation approach that proceeds through the irreversible hydrogenation reaction between para-hydrogen and the substrate.

is a hyperpolarisation approach that proceeds through the reversible hydrogenation reaction between para-hydrogen and the substrate.

is a hyperpolarisation approach that does not proceed through irreversible chemical reaction between para-hydrogen and the substrate; the metal catalyst acts as polarisation facilitator.

is a hyperpolarisation approach that relies on direct polarisation transfer between para-hydrogen and the compound of interest.

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