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ACD/Labs Blog

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
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...

Arvin Moser
Rings plus Double Bonds Equivalent (RDBE) (also known as the degree/element of unsaturation or index of hydrogen deficiency) can be determined from a Molecular Formula (MF). The calculation provides insight into the number of rings and/or double bonds and/or triple bonds to expect from an unknown structure. RDBE = (# of C) + 1 –...

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
Without any structural information, we can estimate an upper limit on the number of carbons using the m/z for the molecular ion. For the molecular ion at m/z 386.4 Da (shown in the mass spectrum below), the upper limit on the number of carbons is calculated at 386.4 / 12 = 32.2. Rounding down, we...

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...