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ACD/Labs Blog

Arvin Moser
A window function (also known as apodization function or convolution) is applied to an FID to emphasize a region of the FID over another. The general goal is to improve the SNR (Signal-to-noise) ratio. The early stages of processing such as applying the “correct” window function can affect the time spent on an elucidation especially...

Arvin Moser
Depending on the experimental conditions, signals from exchangeable protons such as NH and OH can be present on a 1H NMR spectrum. A key to interpreting a 1H NMR is distinguishing between CHn protons (where n = 1, 2 or 3) and exchangeable protons. Acquiring an 1H-13C 2D NMR experiment can assist in this process,...

Arvin Moser
1H-1H couplings arise from influences on a proton’s magnetic field induced by the magnetic field of a neighbouring proton(s). As a proton experiences coupling from a neighbouring proton, so too is the coupling reciprocated to the neighbouring proton(s). By measuring the J-coupling for each splitting pattern, the proton connectivity information can be deduced. By comparing...

Arvin Moser
Proton-proton couplings arise from influences on the proton’s magnetic field from the magnetic field of neighbouring protons. Being capable to recognize among the vast array of coupling patterns can facilitate the time spent on interpreting a 1H NMR. The diagram below illustrates two coupling patterns: a triplet of doublets (td) and a doublet of triplets...

Arvin Moser
I got some great comments from Tony and Gary on the “Dealing with a Mixture…” post that I decided to do a follow-up post. http://acdlabs.typepad.com/elucidation/2008/02/dealing-with-a.html In my lab days, I would routinely workup a newly acquired 1H NMR for an unknown sample prior to acquiring a 2D NMR dataset. One of my goals was to examine...

Ryan Sasaki
Back to the chemists with their ELN who continue to resort to their paper spectra. Is it just an old habit? No. I think it is something else. In fact I think there are two major (and completely understandable) reasons why some chemist continue to resist the complete transition to the electronic world: One of...

Ryan Sasaki
This is the topic I will be presenting on at our annual ENC Symposium on March 9, 2008. If you happen to be attending this conference in Asilomar, check out the agenda and register here. I mentioned this before, but I follow the Depth-First Blog authored by Rich Apodaca rather closely and I highly recommend...

Arvin Moser
As would-be elucidators dive into an elucidation for an organic unknown, narrowing down a single molecular formula (MF) becomes vital in simplifying the elucidation. However, one hurdle quickly leads into another. As the total atom count adds up, the number of possible isomers increases just as much (See Table and Graph below). I can’t imagine...

Arvin Moser
One of the hardest parts of interpreting an NMR dataset is separating peaks from a mixture of compounds. To illustrate this point, below are the aromatic regions of two 75 MHz 13C NMR run on a mixture of methylbenzene and ethylbenzene in CDCl3. If the mixture exists at an approximate 1:1 ratio (top figure), then...

ACDLabs
Let me begin by stating my experiences with elucidations on organic molecules. I have led over 60 training sessions attended by chemists and Spectroscopists from Academia to industry around the world. Some more successful than others—this came down to expertise of the attendee. I have also conversed with dozens of chemists/Spectroscopists, experts and non-experts, at...