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ACD/Labs Blog

Arvin Moser
Long range 2D NMR experiments do not necessarily provide information about all the connectivities. The following structure elucidation problem set is one such example. Based on the 1H-13C HMBC shown below, there is no evident correlation between the 1H at 5.31 ppm and the 13C at 21.1 ppm. Note the green box describes the region...

Arvin Moser
Typical for long range 2D NMR experiments, spectral data may exhibit more than one correlation for two coupled nuclei (e.g. A to B and B to A). The pairwise correlations offer an extra degree of confidence in the interpretation. For the following fragment, an 1H-13C HMBC correlation exists for the 1H 2.15 ppm to 13C...

Arvin Moser
Like any new process, it takes some practice to extract, understand and convert the information presented from a set of experimental NMR datasets into a fragment. The only fragment that can accommodate the set of restrictions from a 1H-13C HSQC and HMBC is 2,3-dimethylbutane-1,1-diyl. The green arrows illustrate the 2-3JCH coupling responses extracted from an...

Arvin Moser
The goal of this puzzle is to conceptualize a fragment(s) from the given information. In the following example, a set of protonated sp3 carbons were extracted from an HSQC experiment (not shown). The green arrows represent the 2-3JCH coupling responses extracted from an HMBC experiment. Based on these restrictions, what fragment(s) supports the data? Note...

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...