The Attached Proton Test (APT) is a very useful experiment that, like DEPT, provides information about how many hydrogens or protons are attached to a particular carbon atom. Both DEPT and APT do this by “editing” the spectrum so that the carbon signals point either up or down depending on the number of attached hydrogens. APT differs from DEPT in several significant ways, though. The first is that quaternary carbons (i.e. carbons that bear no hydrogens) are retained in the APT spectrum, whereas they are absent in DEPT (though there are variants of the traditional DEPT experiment that do retain the quaternary signals). In APT, quaternary and methylene carbons point down by convention, while methyl and methine carbons point up. Figure 1 shows a comparison of a conventional carbon, APT and DEPT-135 spectra of a sample of propyl benzoate.
Fatty acids consist of long carbon chains ending with a carboxylic acid on one side and a methyl group on the other. Most naturally occurring fatty acids have an even number of carbon atoms and can be either saturated or unsaturated. Unsaturated fatty acids have one or more double bonds between carbon atoms. Typical fatty acids found in vegetable oils are saturated palmitic acid (C16:0) and stearic acid (C18:0), as well as oleic acid (C18:1) with a single double bond starting at carbon nine (omega-9), linoleic acid (C18:2) with two double bonds starting at position 6 (omega-6), and alpha-linolenic acid with three double bonds starting at position 3 (omega-3). (more…)
The group of Professor Yoshida at the Department of Synthetic Chemistry and Biological Chemistry of Kyoto University has recently published an article showing how Spinsolve benchtop NMR spectroscopy can be used to optimise the reactions of aminating reagents to achieve an efficient C–N bond formation without using any catalyst.
Two recent publications (link here and here) in international journals highlight the potential of using the Spinsolve benchtop NMR for real time chemical reaction monitoring. Interest in using NMR spectroscopy to monitor chemical reactions has been increasing as the information can be used to optimise yield and minimise waste in order to enhance sustainability of the production process.
One of papers from the Ley group at Cambridge University (Musio et al., ACS Sustainable Chem. Eng, 2017) describes how real-time reaction monitoring on Fluorine can be used to optimise the reaction and reduce the environmental impact in the synthesis of functional fluorinated products. The other paper from the Blümich group at RWTH Aachen (Singh et al., Anal. Bioanal. Chem., 409, pp 7223–7234, 2017) evaluates the on-line benchtop NMR reaction monitoring method against off-line GC and high-field NMR methods and finds excellent agreement between them.
Assigning peaks in the NMR spectrum is a fundamental part of structure verification. Depending on a variety of factors including the size and complexity of the molecule, and the field strength the NMR data are collected at, this can be a straightforward exercise or an extremely challenging one! For example, in the case of a fairly simple compound like lidocaine, it is relatively easy to assign all of the peaks directly in the 1H spectrum using a 43 MHz benchtop NMR spectrometer. However, as a compound’s molecular weight increases so the spectra tend to become more complex, with more resonances and, inevitably, more signal overlap. Assigning the peaks thus becomes significantly more challenging, which is where collecting 2D NMR spectra can help with completing the assignments.
Wageningen University & Research (WUR) is formed from the collaboration between Wageningen University and the Wageningen Research foundation. With the mission “to explore the potential of nature to improve the quality of life,” its staff and students work in the domain of healthy foods and living environments. Dr Teris van Beek is a Lecturer in the Department of Agrotechnology & Food Sciences. Among his responsibilities is the coordination of the undergraduate course in analytical chemistry where 220 molecular life sciences and biotechnology students are introduced to practical spectroscopy each year (UV, IR, MS, NMR, structure elucidation).
Due to their high retail value, some edible oils are often blended wilfully with other more inexpensive vegetable oils. Two recent publications by Kim et al. and Krause et al. in international journals were able to demonstrate that Spinsolve 1H benchtop NMR spectroscopy is a possible cost-effective method for discriminating the authenticity of some vegetable oils.
Overlaid 60 MHz 1H‑NMR spectra of genuine patchouli oils spiked with 9 different adulterants at 20%.
Professor Mike Johns at the University of Western Australia shared this story about doing NMR outdoors with one of their Spinsolve spectrometers. The outdoor environment presents a number of challenges for any analytical instrument and not normally a place you would find NMR spectrometers. Great to hear the trial was successful. Details and pictures below.
In collaboration with Chevron and Woodside, the Fluid Science and Resources Research Group at the University of Western Australia (UWA) trialled a ppm oil-in water measurement protocol built around solid phase extraction and a Magritek 1H 43 MHz Spinsolve benchtop NMR spectrometer. This occurred in October 2017 on the Woodside Pluto LNG plant in North West Australia. Measurements were performed outside, adjacent to the waste water treatment plant, using the SPE-NMR apparatus shown below. The trial was successful with measurements being consistent with laboratory data over a two week period.