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ACD/Labs Blog

Arvin Moser
When dealing with a structure elucidation problem where little or no previous fragment information exists, the number of possibilities can seem endless. Although typically one envisions a neutral compound for the unknown, ionic compounds, such as salts and zwitterions, are also just as likely and thus can add to the complex nature of an elucidation....

Arvin Moser
A common misinterpretation of 2D NMR data can occur when dealing with weak correlations. Weak correlations are commonly introduced in how the sample is prepared or how the data is collected or processed. Examining the spectrum down to level of the density matrix can ensure all correlations are picked up. The 1H-13C HMQC below shows...

Arvin Moser
When presented with an NMR dataset, a highly-experienced elucidator can interpret the dataset without any direct need to do peak picking, integration and multiplet analysis through software. (This may not be the case every time as severe peak overlap can complicate matters.) In essence, this NMR interpretation skill equates to speed reading and can be...

Arvin Moser
Carbon peaks that overlap on an 1H -13C HMBC experiment can be tricky to deal with especially when additional experiments do not help to clarify the situation. A good approach is to keep note of any high correlation counts for a carbon resonance, and subsequently, treat the carbon resonance as possibly multiple carbons with coincidental...

Arvin Moser
In NMR, nuclei can be classified as isochronous or anisochronous. “Where diastereotopic protons show the same chemical shift, they are said to be accidentally equivalent or isochronous, and where they have different chemical shifts the protons are described as anisochronous.” Stereochemistry by David G. Morris, Royal Society of Chemistry (Great Britain) Published by Royal Society...

Arvin Moser
Certain experimental conditions, such as varying the temperature or using different solvents, can influence the interpretation of NMR data. Although it can be useful to collect data with different solvents (e.g. DMSO-d6 or Chloroform-d) or temperatures to decrease peak overlap in a particular region, it can complicate the structure elucidation process by increasing the amount...

Arvin Moser
When working with multiple NMR datasets, it is key to set a reference point(s) in order to align all the datasets. The elucidation purpose — as opposed to standard NMR purposes of referencing to a standard such as TMS — behind referencing the spectral data to a common point(s) is to facilitate the interpretation and...

Arvin Moser
Like driving a car, the driver navigates the vehicle within the designated lanes on a roadway, thus using the lane markers as a reference. The same can be said when analyzing spectral data. Correctly referencing multiple NMR data is critical in a structure elucidation process. For the case where 1D and 2D NMR data is...

Arvin Moser
Among intense NMR resonances, weak resonances can be easily overlooked. This is commonly seen with 1H NMR spectra whereby 1H resonances with complicated couplings are spread out over a larger area in comparison to uncoupled 1H resonances that appear as sharp signals. The 1H NMR spectrum below shows 3 intense resonances at 2.39, 2.66 and...

Arvin Moser
The best use of a set of tools for a structure elucidation are those that have a general target or goal in mind. Random experiments for the sake of collecting data are a sure sign of inexperience. With that said, Infrared (IR) spectroscopy is a great tool for identifying or confirming a functional group(s). It...