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ACD/Labs Blog

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...

Arvin Moser
One of the trickiest parts of interpreting NMR data is identifying what signal belongs to the unknown compound and what can be classified as an impurity. In this case, impurities are described as extra signals coming from a solvent(s), a side product(s), extraction/purification process, etc. The 1H NMR spectrum below is for an unknown compound....

Arvin Moser
A deuterated solvent can impact whether exchangeable protons, such as OH or NH, are visible on a 1H NMR spectrum. The advantage of eliminating any contribution from an exchangeable proton(s) is to simplify spectral interpretation. One disadvantage of not seeing exchangeable protons is the deficiency to the total proton count in establishing the molecular formula....

Arvin Moser
Misconstrued coupling patterns on a 1H NMR spectrum can halt an elucidation process in its track. As such, structural connectivity is best validated with additional data such as a 1H-1H COSY. A good use of coupling patterns and coupling constants is at the end of the elucidation process. Candidate structures can be verified or eliminated...

Arvin Moser
Peak shape, and subsequently the observed coupling pattern, is highly dependent on a range of factors such as temperature, concentration, pH, FID processing, etc. Relying solely on a 1H NMR spectrum for structure determination can lead into the risky realm of misinterpreting a coupling pattern. One of the simplest solutions to most elucidations is to...

Ryan Sasaki
This is a continuation of a series of posts that began here. In the previous post of this series, I discussed how chemists can extract multiplet reports in journal format on the fly using the same procedure to re-cut integrals in the spectrum. Well in addition to having this nice reporting tool, the software can...