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ACD/Labs Blog

Arvin Moser
Characteristic isotopic patterns in MS can assist the elucidator in revealing the presence or absence of atoms. For the Br, Cl, S and Si atoms, a good approach is to examine the peak intensity of the A+2 signal. The respective contributions by the isotopes 81Br, 37Cl, 34S and 30Si are approximately 49.3, 24.3, 4.2 and...

Arvin Moser
There are two approaches to deciding which scenario best fits the NMR data in the puzzle. A structure elucidator can provide evidence that one scenario is more probable than an other and/or eliminate one scenario on the grounds of insufficient/contradictory data to support it. For the following 1H NMR spectrum, if the integral of the...

Arvin Moser
The goal of this puzzle is to distinguish between strong coupling and peak overlap. For the following 1H NMR spectrum, are the 1H signals at 7.58-7.59 ppm exhibiting strong coupling or are they two overlapping multiplets or both?

Arvin Moser
With intense solvent signals present on a spectrum, a smaller signal(s) can easily be missed. If 2D NMR data is available, then this extra information can assist in clarifying whether a small signal(s) is obscured by larger signals. On the 1H-13C HMBC below, the correlations for CDCl3/CHCl3 (due to 1J coupling responses and more) are...

Arvin Moser
‘How many signals are present?’ is such a simple question, and yet, it is a fundamental question to an elucidator. Mistaken a signal or overlook one and the elucidator can run the risk of wasting time and effort.   The 13C [1H] NMR spectrum below shows 3 discernible signals that are attributed to the solvent CDCl3. In...

Arvin Moser
When dealing with small sample concentrations of an unknown compound, the NMR region where a large solvent signal appears rarely gets a second look. However, a large NMR signal can easily obscure a small signal. From one elucidator to another, check the solvent signal for any structural signals. In the 13C [1H] NMR spectrum below,...

Arvin Moser
Based on experience, fused ring systems on an unknown structure tend to conjure up variations of odd connections. The possibilities can seem endless. The diagram, shown below, samples a subset of fused ring systems for a given dataset. It is important to note that although certain systems may be more appealing to the eye, it...

Arvin Moser
Socrates is known for saying ‘Know thyself’, along the same line, chemists should ‘Know thy instrument’. The example below is one such case. The 13C NMR [1H] spectrum below exhibits 6 signals. If an unknown compound comprises of 7 carbon atoms, then the following scenarios, or combinations thereof, are possible to account for missing or extra...

Arvin Moser
Structure elucidation by NMR involves a deep understanding of various technical aspects behind data acquisition. Being aware of how the instrument works can facilitate the process and reduce the aggravation. For today’s puzzle, an unknown compound is known to comprise of 7 carbon atoms and exhibit the following 13C NMR spectrum with 1H decoupling. How...

Arvin Moser
The goal of this puzzle is to determine the respective benzene ring systems that would exhibit the following 1H NMR spectrum. The number of substituted benzene ring systems that would exhibit the following 1H NMR spectrum is 3 (assuming no repeating units). The keys to solving this puzzle lie with the determination of which multiplets...