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ACD/Labs Blog

Arvin Moser
In electrospray ionization MS (ESI-MS), ions are produced by the addition of a proton ([M+H]+). However, in cases where the analyte molecule is already charged, e.g. quaternary amine salts, the resulting ion may be an M+ ion. Two ESI+ mass spectra are shown below. To test whether the molecular ion is M+ or M+H+, deuterium...

Arvin Moser
The underlying essence of a structure elucidation process is to structurally distinguish an unknown from a set of possible isomers. This is evident by the number of possible isomers for a given molecular formula. The chart below divides isomers into two groups: Structural/Constitutional/Regio and Stereo/Spatial isomers. Wikipedia links are included for further reading into the...

Arvin Moser
The previous blog described two general approaches to analyzing data for an unknown compound: broad and focused approaches. The table below lists the general advantages of broad and focused approaches for a structure elucidation. Depending on the data at hand, one approach can be considered the better choice. An elucidation where lots of background information...

Arvin Moser
There are 2 general approaches to handling data for an unknown compound. A. Start from a broad standpoint and work to narrow down the result(s). An example of this approach is to treat uncertain correlations on an HMBC as 4J coupling rather than as 3J coupling. or B. Start at a focused point and work...

Arvin Moser
Just as there are a variety of fishes in the sea, structure elucidators come in a variety of forms. What makes a qualified elucidator good? Yeah, luck and natural talent can play a role sometimes but it is not an exclusive club by any means. A good elucidator is typically ambitious with a wealth of...

Arvin Moser
For a structure elucidation process, applying an apodization (or window function) to an NMR spectrum can be a good thing and sometimes can be a bad thing. Making peaks broader can assist in differentiating signals from noise, but can also cause neighboring peaks to mesh into a single resonance. The best approach in handling spectral...

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...