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ACD/Labs Blog

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...

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
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
MS data collected off an instrument is presented as either profile or centroid mode. Shown below are two mass spectra illustrating an ion cluster for profile data and a centroid mass spectrum created from the profile data. In profile mode, a peak is represented by a collection of signals over several scans. The advantage of...

Arvin Moser
On an MS dataset, the x-axis is a measure of the mass to charge (m/z) ratio. Although it is easy to classify a signal as belonging to a singly charged ion (+1 or -1), one needs to be capable of recognizing a multiply charged (+2, -2, +3, etc.) ion as not to misinterpret the MS...

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...