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ACD/Labs Blog

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
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
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...

Arvin Moser
Yes, it is possible to elucidate an unknown with just a 1H NMR spectrum but only for specific cases*. Case 1: an unknown with a low molecular weight and a “well-resolved” 1H NMR spectrum. Case 2: the unknown has been identified previously, or at least part of it, in a database/library/literature and a spectrum search...

Arvin Moser
One of the trickiest parts of interpreting a 1H-13C HMBC is deciding whether a 13C resonance is coinciding with another 13C resonance, i.e. overlapping 13C peaks. A past blog, Part 1, describes a specific case where the possibility of two coinciding 13C resonances can be deciphered based on a high carbon correlation count. Herein, we...