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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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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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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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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