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ACD/Labs Blog

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
The progression of a structure elucidation process is to examine the experimental data, compare the results to literature if possible, build a set of fragments based on the available data and finally assemble the fragments until a candidate structure(s) is reached. The assembly part is very much like working on a jigsaw puzzle. When all...

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
Failures, as are successes, are an integral part of a structure elucidator’s role. What differentiates a good elucidator from a bad one is the capability of an elucidator to learn from his/her failures. The most common obstacle that can hold a structure elucidation process from becoming a success is structural bias. (This is based on...

Arvin Moser
Attempting a challenging structure elucidation of an unknown and being unable to solve the problem can put a damper on a hectic workload and possibly on your skills as an elucidator. Emotionally, the excitement of working on a challenging elucidation problem leads into frustration — results are what count. Subsequently, the elucidator faces the following...

Arvin Moser
Here is a lesson I learnt over time while working on small molecules—my Elucidation Evolution. Thinking back to when I started doing elucidations of unknowns, my mindset was to collect loads of data (NMR, MS, IR, etc.) whether I needed it or not. Initially inexperienced, I was extracting bits and pieces of information from various...

Arvin Moser
A biased elucidation is an elucidation where the chemist makes certain assumptions about the data at hand based on a previous experience(s) and not deviating from it. Depending on the elucidation, it can be a good thing or a very bad thing. As a good thing, it can speed up the time spent on an...