Getting COSY with the TOCSY Experiment

Getting COSY with the TOCSY Experiment

2D NMR experiments can provide a wealth of information to aid in the structural elucidation of chemical compounds. Of the many 2D NMR experiments available, the homonuclear correlation spectroscopy (COSY) sequence is one of the most popular and is used to identify which spin systems are directly coupled to each other. As an example, the 1H-1H COSY spectrum of 1-propanol recorded on the NMReady-60 is shown below in Figure 1.

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Beyond Structural Elucidation - Introduction to qNMR Part III - Relaxation Delays

Beyond Structural Elucidation - Introduction to qNMR Part III - Relaxation Delays

In this blog, Part III of the qNMR series, I will be addressing relaxation and why it's important for quantitative nuclear magnetic resonance (qNMR) experiments. If this is your first time reading about qNMR and would like to know more, please check out our other posts where you can find a general introduction to qNMR as well as information for the types of calibrants available for qNMR experiments.

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What's the 'ism' of today? Keto-Enol Tautomerism

What's the 'ism' of today? Keto-Enol Tautomerism

Tautomers are constitutional isomers that interconvert into each other by an exchange reaction, most commonly a proton transfer. Such two isomers can for example be a ketone and an enol. Keto-enol tautomerism (KET) becomes possible when there are hydrogen atoms adjacent to a carbonyl group (these hydrogen atoms are called α hydrogens). This tautomerism is depicted in Scheme 1 and is also discussed more here.

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Enantiomers – Image | Mirror Image

Enantiomers – Image | Mirror Image

Chirality has a huge impact on the chemistry of a molecule. Due to potentially different physiological effects, pharmaceutical compounds are often used as enantiomerically pure compounds. One enantiomer can act as a healing agent, the other might be toxic to humans. Crazy, right? It makes sense, if you think of how pharmaceuticals work in principle. They bind to receptors, which trigger something in the brain or somewhere else in the human body. These receptors have a special chemical specificity and only the active compounds fit and bind correctly with it. A receptor is a 3D body and thereby is dependent on the stereochemistry of the compounds.

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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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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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Unlocking the Key to Enzymes: Studying Enzyme Kinetics

Unlocking the Key to Enzymes: Studying Enzyme Kinetics

By virtue of its quantitative nature, NMR spectroscopy is increasingly becoming the method of choice to monitor a reaction and determine its kinetic parameters. We’ve demonstrated the ability of the NMReady-60 to monitor a reaction and subsequently extract kinetic parameters in a previous blog post. In this blog post, I’d like to show how the NMReady-60 can be used to study enzyme kinetics. Adapted from a Journal of Chemical Education article published by Olsen and Giles, the enzymatic hydrolysis of N-acetyl-DL-methionine by porcine acylase was studied.

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