Physical Methods and Techniques: NMR Spectroscopy

Edgar, Mark

doi:10.1002/chin.200752280

Cited by 1 publication

(2 citation statements)

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“…However, it is important to include additional coupling constant parameters in such evaluations, since the magnetic inequivalence of the A and A′, and B and B′, nuclei gives rise to significant couplings between them, i.e., on the order of approximately 1−2 Hz. Once the long-range 4 J AC , 4 J A′C couplings of ∼1.22 Hz and 5 J AB′ , 5 J A′B couplings ∼0.6 Hz are included, then the 1 H NMR spectrum can be accurately calculated and predicted at any magnetic field. The chemical shift (ppm) of the AA′, BB′, and C nuclei remains the same at both 400 and 60 MHz magnetic fields (indeed at any magnetic field).…”

Section: ■ Chemical Shifts and Coupling Constantsmentioning

confidence: 99%

“…Currently, many novel applications are being explored for NMR spectroscopy, particularly with regard to the miniaturization of "state-ofthe-art" rapid analytical monitoring technologies. 5 many universities have now invested in low-field, benchtop NMR spectrometers and utilize them in chemistry undergraduate teaching experiments 9−11 in order to determine reaction progress and product purities, for example. The value of the student experience that comes with direct access to a benchtop NMR instrument, however, must be considered when the purchase price is discussed; the cost of these facilities lies between $20K and $70K.…”

Section: ■ Introductionmentioning

confidence: 99%

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Benchtop NMR Spectroscopy and Spectral Analysis of the cis- and trans-Stilbene Products of the Wittig Reaction

et al. 2019

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Benchtop NMR spectrometers are now becoming more widely employed in university teaching laboratories. These low-field instruments are increasingly used in reaction monitoring and product purity applications. NMR spectra obtained using these spectrometers (40-80 MHz) tend to suffer from significant overlap of signals when compared to those obtained at 300-400 MHz or above, and therefore some reactions may be less suited to analysis using such benchtop systems. Whilst some 15 reactions can be modified to make them more amenable to analysis on low-field benchtop spectrometers, the fact remains that many common undergraduate laboratory chemistry reactions remain as a stalwart of the university education system. Therefore, there is currently a major requirement for benchtop NMR analysis to improve in order to facilitate student understanding.Herein, it is demonstrated a combination of spectral analysis and simulation at low-fields (40-80 20 MHz) that allows the fine structure of second-order effects and overlapping spectra to be deduced, enabling an improved understanding of the low-field benchtop NMR technique within undergraduate student cohorts. The evolution of well-resolved and distinct multiplets at 400 MHz to complex, overlapping multiplets at 40-80 MHz also serves as a useful guide for laboratory demonstrators and academic staff when explaining the advantages of such benchtop systems. The 25 Wittig reaction has been a standard reaction practical session in many university teaching laboratories since the 1980s, the products of which are a mixture of cis-and trans-stilbenes. This reaction serves as an ideal example of how benchtop NMR and analysis can support chemistry teaching laboratories.

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Section: ■ Chemical Shifts and Coupling Constantsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%