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ACD/Labs Blog

Arvin Moser
The line shape of a peak on a chromatogram can offer some insight into the presence of a functional group. However, issues with the instrument are also known to affect the line shape for a peak. The GC/MS EI+ Total Ion Chromatogram/Current (TIC) below shows five peaks. All of the peaks with the exception of...

Arvin Moser
Where a COSY or TOCSY spectrum can be a challenge for a structure with severe spectral overlap, collecting an HSQC-TOCSY spectrum can be a better choice. An HSQC-TOCSY experiment stands for Heteronuclear Single Quantum Coherence-Total Correlation Spectroscopy and other variants include HMQC-TOCSY, HSQC-COSY, etc. Depending on the mixing time, the hybrid experiment generally offers information...

Arvin Moser
Part 1 of the series Teaching and Learning by Spectral Data explored the difference between presenting an NMR problem set to a student in the form of an alphanumerical text or as an actual NMR spectrum. Continuing on the same problem set, another issue arises. Is the information on the elements and the 1H NMR...

Arvin Moser
There are many ways to teach the process of elucidating unknown structures. Offering a student a visual guide, such as seeing firsthand a spectral dataset, can enhance the learning process and better equip the student on future work. Presented below is a typical elucidation question from a university test. The numerical values have been extracted...

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...

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