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ACD/Labs Blog

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...

Arvin Moser
As with many nitrogen-containing compounds, 15N chemical shift information can be critical in elucidating or confirming a candidate structure. Many elucidators extract 15N chemical shifts from such experiments as 15N NMR, 1H-15N HSQC or 1H-15N HMBC. Below are two tautomers, from a previous blog, that differ in the hybridization state of the nitrogen. The 15N...

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...

Arvin Moser
Like a COSY experiment, an HMBC dataset offers many combinations of atom connectivity. The goal for the elucidator is to assess each correlation and narrow down a set of fragments that support the data. For every correlation in a 1H-13C HMBC spectrum, an elucidator must decide whether a correlation corresponds to a 2J, 3J or...