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ACD/Labs Blog

When presented with an NMR dataset, a highly-experienced elucidator can interpret the dataset without any direct need to do peak picking, integration and multiplet analysis through software. (This may not be the case every time as severe peak overlap can complicate matters.) In essence, this NMR interpretation skill equates to speed reading and can be...

A previous blog described the Internet as a valuable tool in searching for previous work based on a molecular formula. In addition to searching the Internet “directly”, certain online sites can assist and facilitate the search process. Some of these sites are free while others have a fee. Be aware that the Internet is full...

One of the really nice things that has been available in our software for many years has been the ability to characterize multiplet patterns and coupling constants and to quickly generate a multiplet report like this one: 1H NMR (400 MHz, DMSO-d6)  ppm 0.96 (t, J=7.30 Hz, 3 H) 1.27 (t, J=7.18 Hz, 6...

Searching for unknowns across an internal library or database can serve as a major time saver. A more accessible database is the Internet. Many chemists and elucidators search the World Wide Web using a mass, a molecular formula or a fragment. Be aware that proprietary data sent over the Internet runs the risk of being...

For several years many customers have shown me different ways in which they like to report the interpretation of an NMR dataset. While there have certainly been a variety of different approaches, the most common way I have across looks similar to this: You’ll also find a similar reporting style in journal articles such as...

In a previous blog, the atoms C, H, O, and N were limited to a specific range, 0-50, 0-100, 0-10 and 0-10, respectively. Starting from a wide atom count range ensures molecular formulae are not overlooked. The ranges for the atom count can be restricted further using additional information such as NMR, IR, etc. A...

With a monoisotopic mass identified from a mass spectrum, the next step is to fit a molecular formula (or elemental composition) to the unknown. For organic compounds, the starting elements of choice are Carbon, Hydrogen, Oxygen, Nitrogen and sometimes Sulfur. Information from starting material and known derivatives can also help when deciding what elements and...

Depending on sample preparation, adduct ions can be present on a mass spectrum. The goal of the elucidator is to identify whether an adduct ion(s) is present and its contribution to the mass (or elemental composition) of the unknown compound. The example ESI+ mass spectrum below exhibits 2 ion clusters at m/z 951.305 and 973.287,...

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...

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...

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