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ACD/Labs Blog

Ryan Sasaki
Reality #1: LC/MS has become the primary analytical check for the medicinal chemist. I Love NMR, but it’s the reality So how did we get here? Clearly there a lot of reasons, but one of my hypotheses is based on the evolution of open access and the walk-up environment. No doubt that moving away from...

Arvin Moser
If an elucidator is too successful differentiate an impurity signal from a signal belonging to a compound-of-interest, then the following may be useful: foreknowledge of the prep work, experience with similar compounds and impurities, variations within the spectral data, trial-and-error, etc. From the 1H NMR spectrum, the integral of the 1H signal at 2.52 ppm...

Ryan Sasaki
Reality #1: LC/MS has become the primary analytical check for the medicinal chemist. I Love NMR, but it’s the reality Reality #2: More often than not, NMR spectra are merely glanced at: Sometimes interpretation is based on the presence or absence of one peak (did my reaction go to completion?) How often are NMR spectra...

Arvin Moser
Even with ‘good’ data, every elucidation of an unknown offers the potential for impurities to hinder the process. The task develops into differentiating signals pertaining to an unknown from the impurities. The 1H NMR and 1H-13C HSQC spectra below are for an unknown (solvent signal not shown). Are all the signals from a single unknown...

Arvin Moser
An effective elucidator is capable of connecting information from multiple sources with the goal of eliminating the inconsistent candidates. In this puzzle, the candidates are molecular formulae (MFs). The previous blog listed 4 potential MFs differing in mass difference and RDBE. The mass difference is not a good filter as the mass differences for the...

Arvin Moser
When the spectral data is sparse, the list of potential candidate structures can seem endless. The task then becomes sifting through the spectral data as a means to filter the candidates. The purpose of this puzzle is to perform such a task. The following unknown compound with a mass of 380.1 +/- 0.5 Da comprises...

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
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...