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ACD/Labs Blog

Arvin Moser
With a well-tuned and calibrated, high resolution MS instrument, a molecular formula(e) can be devised from the m/z for an ion peak. In cases where more than one molecular formula fits, knowing the accuracy of the MS instrument can help in narrowing down the choices. The first step is to identify the molecular ion peak...

Arvin Moser
When interpreting data from a 1H-13C HMBC without a high-resolution 1D 13C NMR, there is the possibility to miss coincidental overlapping carbons. As such, always consider a missing carbon or two as part of the structure elucidation for an unknown. The 1H-13C HMBC below—note the lack of a high-resolution 1D 13C NMR spectrum—exhibits a 2-3J...

Arvin Moser
I would like to begin the new year with a weblog that summarizes the components of an elucidation process. Each component, shown as a Venn-like diagram below, can blend in with the next until a conclusion is reached. The goal for the elucidator is to exhaust all aspects of each possible component thus ensuring that...

Ryan Sasaki
As I mentioned in my last post, with the release of Version 12 out of the door, there are many new and exciting things to explore in our latest release outside of the NMR Workbook. For me, one of the things that I continue to be amazed about are how much the little things matter...

Arvin Moser
When peak picking a 2D NMR experiment, past weblogs have advocated zooming in on correlations especially in cases dealing with ambiguity. Depending on the data collection parameters, a 1H-13C HMBC experiment can contain paired 1J coupling responses. Without careful scrutiny of the data, these extra responses can be misinterpreted as long-range correlations (2J or longer). The...

Arvin Moser
Many organic chemists employ Mass spectrometry (MS) as a convenient verification tool for their product in a synthetic reaction. Derivatization such as adding a protective (or protecting) group can often be detected by MS. The EI mass spectrum for tert-butyl 3-aminopiperidine-1-carboxylate is shown below. The ‘terminal’ atoms belonging to the protective group, tert-Butyloxycarbonyl (BOC or...

Arvin Moser
Infrared (IR) spectrometry is an excellent diagnostic tool for identifying, or lack of, a carbonyl functional group(s). Carbonyl stretching vibration absorbs between 1900-1600 cm-1—a region where few other functional groups absorb. In addition, the carbonyl vibration is typically intense and thus easy to spot. The gas phase FT-IR spectra, shown below, represent five carbonyl bands...

Arvin Moser
Infrared (IR) spectrometry can serve as a simple method to gather information on the presence of OH. Characteristic OH absorptions occur around the ranges of 3700-3200 cm-1 (OH stretching) and 1200-1000 cm-1 (OH bending). In the case of hydrogen-bonded OH, the band in the region 3700-3200 cm-1 generally appears broad and sometimes can go unnoticed....

Arvin Moser
Like bromine, compounds that contain chlorine atoms have a distinct ion pattern on a mass spectrum. The A+2 peak for a monochlorinated compound will be at almost one-third the intensity to the 35Cl peak due to the presence of 37Cl isotope. A compound with two chlorine atoms will show distinct A+2 and A+4 peaks with...

Arvin Moser
For synthetic reactions where rearrangement, derivatization, or cyclization has occurred, a common task is to compare the NMR spectra between the starting material and the product. The similar peaks indicate a structural region where change has not occurred whereas the unique peaks indicate a region where change has occurred. Arguably, this becomes a peak mapping...

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