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ACD/Labs Blog

Arvin Moser
Peak matching involves the process of comparing spectral data from a parent or starting material to an unknown compound. (The unknown compound can be referred more specifically as the product, impurity, degradant, metabolite, etc.). The similarities between the data indicate regions that have not changed while the differences indicate regions of change. The full scan...

Arvin Moser
In past blogs, I have ascribed the process of peak matching as an integral part of structure elucidation. In this series, peak matching is demonstrated with the use of MS data. The scheme below shows a parent compound (2-oxo-N,2-diphenylacetamide) with two possible sites for hydrogenation. The potential modified compounds are 2-hydroxy-N,2-diphenylacetamide and 2-hydroxy-1-phenyl-2-(phenylamino)ethanone labeled A...

Arvin Moser
When you work on enough NMR datasets, eventually you will run into cases where peaks are overlapping. One approach is to apply a peak deconvolution (or fitting) algorithm in an attempt to separate out the contribution of each overlapping peak. The 1H NMR spectrum below shows a multiplet (dd) nearly buried by a large water...

Arvin Moser
In the blog series entitled Distinguishing Impurities, several types of NMR experiments were outlined to offer some insight into what to be on the look out for. Although there is no set guideline in this process, the best advice I may offer is to keep track of all the solvents, be aware of the possibility...

Arvin Moser
Although a 1H-13C HMBC experiment may take a long time to collect with adequate signal-to-noise, it can offer an idea as to which signals belong ‘together’. Generally, signals belonging to the same structure leave a trail of connectivity information via long range correlations. If the atoms belong to the same structure, then a typical HMBC...

Arvin Moser
The past few blogs, Part 3 and Part 4, have examined impurity(ies) identification from short-range 2D NMR experiments without much success. If proton singlets, possibly attributed to impurities, are to be distinguished from the main unknown, then long-range 2D NMR experiments may help out by establishing long-range correlations to other atoms. A 1H-1H TOCSY experiment...

Arvin Moser
Certain NMR experiments offer clues to differentiate a signal from the main unknown and from the impurity(ies). Some clues are not as obvious as others and so it takes a little practice to understand what to look for in a dataset. A 1H-1H double quantum filter (DQF) COSY experiment (shown below) is used to filter...

Arvin Moser
In the series Distinguishing Impurities, Part 1 pointed to certain signs in which an elucidator can differentiate a signal as pertaining to an impurity and not to the main unknown. Part 1 also made reference to using 2D NMR data as a practical approach to ascertain whether a signal from a 1H NMR was an...

Arvin Moser
Structure elucidation is a skill learnt through years of practice. One of the best ways to learn is to learn by example. I feel that there is no better way to do this than mentoring through specific scenarios step-by-step. My intentions behind this blog are to offer a unique source for chemists who use a...

Arvin Moser
A previous blog described how integrals and coupling information can assist in discerning an unknown structure signal from an impurity(ies).  Before proceeding to acquire 2D NMR data to confirm the information, there is the option to purify/rewash the sample (assuming there is enough sample to do this) followed by a spectral comparison of the before...