Beyond Structure Elucidation - Introduction to qNMR Part II - Calibrants

Beyond Structure Elucidation - Introduction to qNMR Part II - Calibrants

In my previous blog post, I introduced several concepts that are relevant to the qNMR experiment. In this blog post, I will talk about how to select a suitable calibrant as well as the difference between using an internal and external calibrant.

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Attached Proton Test, an 'APT' experiment for structural elucidation

Attached Proton Test, an 'APT' experiment for structural elucidation

A key step towards elucidating structures with NMR spectroscopy is the assignment of signals to specific groups within the molecule being analyzed. Two experiments, DEPT (Distortionless Enhancement by Polarization Transfer) and APT (Attached Proton Test), are typically used to aid this process with 13C NMR spectra.1 Both experiments are similar in that the number of attached protons (i.e. the multiplicity) is revealed by the phase of the 13C NMR signals. The key difference between the DEPT and APT experiment is that signals for quaternary carbons are observed in the APT experiment.

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Beyond structural elucidation, introduction to qNMR – Part I

Beyond structural elucidation, introduction to qNMR – Part I

Over the last few years, more and more analytical and industrial laboratories have started employing quantitative nuclear magnetic resonance (qNMR) spectroscopy as a tool for content assignment (due to its superb structural elucidation abilities) and quantification of purity in a sample. This is due to the increase in regulations being imposed by governments onto the pharmaceutical and environmental sectors. It has been previously demonstrated that qNMR spectroscopy can give results with less than 1% uncertainty and possibly down to 0.1% if the right conditions are met.

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HSQC – Revealing the direct-bonded proton-carbon instrument

HSQC – Revealing the direct-bonded proton-carbon instrument

2D NMR experiments provide chemists with evidence to clarify and confirm resonance assignment.  Nowadays every organic chemist uses these experiments called COSY, HMBC and HSQC as routine analytics. Basically, with 2D experiments you correlate some kind of information between two 1D spectra. If we correlate two 1D spectra of the same nucleus we are dealing with homonuclear 2D NMR experiments. The most famous representative of this group is the COSY experiment (find theory here and application here).

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4 Industries That Utilize Process NMR Applications

4 Industries That Utilize Process NMR Applications

NMR is a physical phenomenon in which nuclei in a strong and static magnetic field are perturbed by a weak oscillating magnetic field and respond by producing an electromagnetic signal with a frequency of the magnetic field at the nucleus. NMR spectrometers can be used in various sectors that have previously been overlooked. Since these devices can fit in virtually any location and provide point of access to NMR, professional NMR spectrometers are great for all kinds of reasons.

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Lead NMR Spectroscopy

Lead NMR Spectroscopy

For many years tetraethyl lead was used as the principal fuel additive to enhance the octane rating of gasoline. In the mid-1970s the use of this substance was reduced because of the environmental hazards of lead and because it poisons catalytic converters. Nowadays, the main application of lead metal and lead oxide is in lead-acid batteries. In this application the cathode of the cell consists of lead dioxide packed on a metal grid and the anode is composed of lead metal. The electrochemical reaction is shown in the following equation:

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Evans Method with NMReady-60 for understanding 1H NMR of Paramagnetic Compounds

Evans Method with NMReady-60 for understanding 1H NMR of Paramagnetic Compounds

Due to the presence of unpaired d electrons in their metal ions, many transition metal complexes are paramagnetic. The unpaired electrons have a magnetic dipole moment due to their spin and act like tiny magnets, resulting in a small net attraction to an externally applied magnetic field. Unsurprisingly, the presence of paramagnetic ions has significant effects on both the chemical shift and lineshape of the 1H NMR spectrum of transition metal complexes, with the chemical shift range being much wider along with broadening of the signals.

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