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ACD/Labs Blog

Arvin Moser
In addition to using chemical shift information to ascertain a carbon’s proton count (i.e. C, CH, CH2 or CH3), 13C NMR experiments can be set up in a variety of ways to assist with this process. The following simulated spectra compare a variety of 13C NMR experiments for aspartame. Please note that there are variations...

Ryan Sasaki
For several years many customers have shown me different ways in which they like to report the interpretation of an NMR dataset. While there have certainly been a variety of different approaches, the most common way I have across looks similar to this: You’ll also find a similar reporting style in journal articles such as...

Arvin Moser
In a previous blog, the atoms C, H, O, and N were limited to a specific range, 0-50, 0-100, 0-10 and 0-10, respectively. Starting from a wide atom count range ensures molecular formulae are not overlooked. The ranges for the atom count can be restricted further using additional information such as NMR, IR, etc. A...

Arvin Moser
When interpreting data from a 1H-13C HMBC without a high-resolution 1D 13C NMR, there is the possibility to miss coincidental overlapping carbons. As such, always consider a missing carbon or two as part of the structure elucidation for an unknown. The 1H-13C HMBC below—note the lack of a high-resolution 1D 13C NMR spectrum—exhibits a 2-3J...

Arvin Moser
When peak picking a 2D NMR experiment, past weblogs have advocated zooming in on correlations especially in cases dealing with ambiguity. Depending on the data collection parameters, a 1H-13C HMBC experiment can contain paired 1J coupling responses. Without careful scrutiny of the data, these extra responses can be misinterpreted as long-range correlations (2J or longer). The...

Arvin Moser
For synthetic reactions where rearrangement, derivatization, or cyclization has occurred, a common task is to compare the NMR spectra between the starting material and the product. The similar peaks indicate a structural region where change has not occurred whereas the unique peaks indicate a region where change has occurred. Arguably, this becomes a peak mapping...

Arvin Moser
Carbon peaks that overlap on an 1H -13C HMBC experiment can be tricky to deal with especially when additional experiments do not help to clarify the situation. A good approach is to keep note of any high correlation counts for a carbon resonance, and subsequently, treat the carbon resonance as possibly multiple carbons with coincidental...

Arvin Moser
The 1H-13C HMQC, HSQC, DEPT-HSQC, HSQC-TOCSY and HETCOR experiments offer the elucidator information on the proton-carbon connectivity. The interpretation process comes down to 3 basic assignments: the correlation belongs to a methyl, methylene or methine carbon. A methyl or methine carbon exhibits at most a single correlation between the 1H and 13C axes. A methylene...

Ryan Sasaki
A few months back, I referenced Derek Lowe’s excellent blog, "In the Pipeline" Some of the most interesting entries for me are: Backtracking, Necessary, and UnnecessaryI Can Has Ugly Molecules? Oops. One of the take home messages for me, is when Derek says, "False Negatives and False Positives are waiting in your dataset, depend on...

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...