2D NMR Experiments - HETCOR

2D NMR Experiments -  HETCOR

2D NMR experiments can provide an abundance of information for the structural elucidation of chemical compounds. An older example of a 2D experiment is the heteronuclear correlation (HETCOR) sequence. In this experiment, two different nuclei (usually 13C and1H) are correlated through single bond spin-spin coupling, revealing which proton and carbon groups are bonded to each other.

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Two solvents, two different spectra - Aromatic Solvent Induced Shifts

In my opinion, one of the most helpful papers[1]in the field of NMR spectroscopy in Organic Chemistry consists of ‘just’ two tables. In these, the chemical shifts (1Hand 13C) of as many as forty-two common impurities in twelve different deuterated solvents are listed. This is gold! Why? We know, that the signals of one and the same compound can show a rather high discrepancy in its chemical shifts in different solvents. But did you also know, that there is a concept called Aromatic Solvent Induced Shifts (ASIS), which benefits from this fact? 

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Heteronuclear Spin-Spin Coupling on the NMReady-60PRO

Heteronuclear Spin-Spin Coupling on the NMReady-60PRO

Spin-spin coupling is an important facet of 1H NMR spectroscopy, as crucial details about the structure of a molecule are revealed based on the pattern of multiplets observed. In general, the signal for a group of equivalent protons will be split into a multiplet based on the n+1 rule, where nis the number of equivalent protons that are adjacent to the protons. For example, the signal of the CH2 protons in an ethyl group will be observed as a quartet (adjacent to three equivalent protons; 3+ 1) while the signal for the CH3protons in the same ethyl group will be a triplet (adjacent to two equivalent protons; 2+ 1).

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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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