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ACD/Labs Blog

Ryan Sasaki
Recently I finished a great book that made me think about different things on a lot of different levels. The book is called The Black Swan and the author is Nassim Nicholas Taleb. In short, a black swan is defined as an event, positive or negative, that is deemed improbable yet causes massive consequences. From...

Arvin Moser
Couplings can be affected by the torsion angle. The couplings can be expressed mathematically with a cos θ relationship. At certain values of θ, the couplings are expected to be relatively weaker to non-existent. Based on the torsion angle, fragment B is expected to exhibit a prominent coupling between the red and gold nuclei. Fragment A,...

Arvin Moser
For a simple case, the torsion angle (or dihedral angle) is described as the angle between 4 contiguous atoms or 3 successive bonds. In NMR, the magnitude of the coupling is directly related to the torsion angle between the vicinal nuclei (see the Karplus equation for more details). Below are two animations, A and B, for...

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
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
The goal of this puzzle is to resolve the ambiguity exhibited within a 2D NMR spectrum and thus provide the correct signal correlation. Although this exercise may seem a trivial one, it is important to go over the rationale when correlating one signal to another. For the following 1H-13C HSQC-DEPT NMR spectrum it is important...