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ACD/Labs Blog

Arvin Moser
Ideally, identifying whether a fluorine atom(s) is present is as simple as acquiring a 19F NMR. However, running ‘uncommon’ experiments is not usually my first step in an elucidation (MDE). Imagine a scenario where the elucidator is unsure whether fluorine is present. He/she acquires a 19F NMR and sees no 19F resonances. Therefore the extra...

Arvin Moser
When faced with a crowded region in a 1H NMR spectrum, a 2D NMR experiment can assist in removing the ambiguity and in narrowing down the proton count. For the 1H NMR spectrum below, Multiplet F (the region between 1.4 to 1.8 ppm) displays an integral of 6.71. Although several factors may contrbute to the...

Arvin Moser
A very useful bit of information on the proton count comes from integrating a 1H NMR spectrum. However, overlapping resonances can make integration less than straightforward and in some cases ambiguous. Integration involves the following decisions to be made by the elucidator: which resonances to integrate, where the integral begins and ends, and what the...

Arvin Moser
Here is a lesson I learnt over time while working on small molecules—my Elucidation Evolution. Thinking back to when I started doing elucidations of unknowns, my mindset was to collect loads of data (NMR, MS, IR, etc.) whether I needed it or not. Initially inexperienced, I was extracting bits and pieces of information from various...

Arvin Moser
A biased elucidation is an elucidation where the chemist makes certain assumptions about the data at hand based on a previous experience(s) and not deviating from it. Depending on the elucidation, it can be a good thing or a very bad thing. As a good thing, it can speed up the time spent on an...

Arvin Moser
Looking for the next big pharmaceutical drug among natural products is a growing endeavour. However, a common drawback to working with natural products is the limited amount of sample. With a sample limitation, acquiring a 13C NMR spectrum within a reasonable time can be an issue. Rather than wasting instrument time on a 13C NMR,...

Arvin Moser
Following the RDBE blogs, I decided to run a little test pointed out to me by Robin Martin, Ph.D. Without using the RDBE formula, what is the RDBE (number of rings) for cubane (structure shown below)? Starting with the 2D representation of cubane, it comes down to counting how many bonds are removed to displace...

Arvin Moser
The second-order effects (also known as tilting or roofing) exhibited by multiplets can be used to identify multiplets coupled to each other. The 1H NMR spectrum below illustrates an example of strong coupling among three multiplets. The peak intensities across Multiplets A and B are different, that is, the peak on the right side of...

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
In light of the posting by Oliver Fiehn’s group (http://fiehnlab.ucdavis.edu/projects/Seven_Golden_Rules/Ring-Double-Bonds/), I’ve decided to blog some compounds I’ve encountered in the lab. Using the 2nd formula from the previous blog (http://acdlabs.typepad.com/elucidation/2008/03/rings-double-bo.html), for some cases the RDBE calculation will work if the correct atom valence is known. Note: the nitrochloroform compound can be drawn more than one...