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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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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Spine disease? No, just a rigid backbone, but it keeps from flippin’ the ring!

Spine disease? No, just a rigid backbone, but it keeps from flippin’ the ring!

For this one I must begin with a little personal background information due to my special relationship to the scaffold of the target compound. During my diploma thesis I investigated gold(I) phosphine complexes as catalysts for the intermolecular hydroamidation of olefins.[1] I found that dinuclear gold complex showed superior reaction times and yields compared to mononuclear complexes, like Ph3PAuCl. This particular dinuclear complex [xantphos(AuCl)2] (1) was kicking the reaction of norbornene (2) and tosyl amide (3) and made my first academic publication possible (scheme 1).

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Automation, Benchtop NMR and Industry

Automation, Benchtop NMR and Industry

Since it was discovered, the typical trend in NMR Spectroscopy has been towards higher field, evidenced by the rapid replacement of permanent magnets with supercons.[1]  Why?  Well, NMR Spectroscopy, of course, is one of the most information rich molecular spectroscopic techniques available, providing information of the type of nuclei, the number of those nuclei and even how they’re connected.  As you move to higher field you can immediately observe two things: 1) it’s easier to extract the aforementioned information because the resolution is better (i.e., more Hz/ppm dispersion) given the more favourable dispersion and 2) the data has inherently higher signal-to-noise ratio. 

 

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Eat Your Heart Out Mass Spec: Measuring 10B/11B Isotopic Ratio by NMR Spectroscopy

Eat Your Heart Out Mass Spec: Measuring 10B/11B Isotopic Ratio by NMR Spectroscopy

As I’m sure the readers of this blog know, NMR spectroscopy is used widely across all branches of chemistry due to its powerful structure elucidation capabilities and the inherently quantitative nature of the technique.  Organic relies primarily on 1H/13C  experiments where as inorganic chemistry can expand to other nuclei, like 31P and 11B.  However, there are many other applications for NMR other than just structural elucidation.  Perhaps a lesser known application of NMR spectroscopy, is its ability to determine the isotopic ratio of elements! In this blog post I would like to demonstrate a novel method to determine the 10B/11B isotopic ratio using our NMReady-60e and 1H NMR spectra! 

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Nucleophilic Substitution Reactions and Benchtop NMR

Nucleophilic Substitution Reactions and Benchtop NMR

Nucleophilic substitution reactions are frequently performed as an experiment in undergraduate organic chemistry courses. Reactions taking place at saturated carbons are mainly classified as SN1 or SN2, where S stands for substitution, N for nucleophilic, and the number indicates the molecularity of the reaction (1 for a unimolecular process, 2 for a bimolecular process). In the SN2 reaction the attack of the nucleophile and elimination of the leaving group occur simultaneously in a concerted process and its rate is proportional to the concentration of both the alkyl halide and the nucleophile.

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