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ACD/Labs Blog

Arvin Moser
In the constant pursuit of new pharmaceutical drugs, process chemists (sometimes referred to as medicinal or synthetic chemists) must investigate all impurities detected in a new drug manufacturing process. The chemist’s procedure is simple: identify, elucidate and synthesize each and every single impurity. The chromatogram (UV detector set at 254 nm) below shows three peaks....

Arvin Moser
After a long and arduous attempt at an elucidation, it is quite common to be left with more than one candidate structure. In some cases collecting more data is not an option and an exhaustive database/literature search turns up nothing useful, the alternative approach is to synthesize the proposed candidates and then compare the spectral...

Arvin Moser
Datasets for large unknown compounds tend to be complicated and typically require a lot of effort in distinguishing one signal from another. Having some background information about the unknown, such as a metabolite, a precursor, a derivative, etc. can be invaluable with the detail work needed to get through an elucidation. The 13C NMR spectrum...

Arvin Moser
With any type of data, there is an inherent risk of misinterpretation. My advice to elucidators is to consider multiple solutions and examine each one thoroughly. In the end, the answer to any problem set lies in tying together the bits of information in hopes of understanding the bigger picture. Recap of the problem: The...

Arvin Moser
Pattern recognition is an integral part of the process of structure elucidation. The quicker the elucidator can pick up on the pattern, the faster the elucidation can be accomplished and the less time wasted in elucidating the unknown. Recap of the problem: The ESI+ MS shows a single [M+H]+ at m/z 102 allowing a maximum carbon...

Arvin Moser
Whenever data appear to contradict each other, an instinctive reaction to this problem is to collect more data. Collecting more data can help to understand the problem and/or complicate the matter. Remember the model for Elucidation Evolution? Maximize data extraction (MDE) while minimizing data collection (MDC). Recap of the problem: The ESI+ MS shows a...

Arvin Moser
Structure elucidators will routinely use data from multiple techniques such as MS and NMR to build a proposed structure(s). When dealing with data from multiple techniques, the issue may arise that the data seem to contradict each other. In these cases, it is best to step back and re-evaluate the data from a different angle....

Arvin Moser
NOESY, ROESY, COSY and TOCSY are all 2D NMR experiments that sound so similar but offer different pieces of information about the puzzle. When interpreting the NMR data, it is important to understand how the nuclei interact with each other. For example, the presence of a cross peak (a correlation off the diagonal) on a...

Arvin Moser
Several NMR experiments offer tools to help determine the stereochemistry of a structure. Some typical experiments are 1D NOE (Nuclear Overhauser Effect), 2D NOESY (NOE Spectroscopy) and ROESY (Rotating-frame Overhauser Effect Spectroscopy). These experiments will produce signals for nuclei that are close to each other through space independent of the number of bonds separating the...

Arvin Moser
Tandem mass spectrometry involves the process of selecting and separating a product ion(s) (or daughter ion(s)) and fragmenting it in a second mass analyzer. This is commonly referred to as MS/MS or MS2. Additional tandem processes can be applied to ions in the MS/MS data to create MS3 data, and so forth. The metabolites A...