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ACD/Labs Blog

Arvin Moser
Yes, basic counting is important in solving an unknown. How did you stack up with this puzzle? The 13C NMR spectrum below shows 7 signals in total, 3 intense signals and 4 weak signals. The 4 weak signals follow a quartet pattern produced by a CF3 group. The unknown contains a minimum of 4 C...

Arvin Moser
Coupling information is very useful in locating the position of an atom in relation to other atoms. This puzzle covers one such example. For an unknown compound1, the 13C assignment is not clear for carbons 116 or 134 ppm. The 13C NMR spectrum shows the 19F-13C coupling for the carbon at 116 ppm as 23.7...

Arvin Moser
Coupling information is very useful in locating the position of an atom in relation to other atoms. This puzzle covers one such example. For an unknown compound1, a di-substituted phenyl ring with a fluorine substituent was deciphered. The 13C NMR spectrum below shows two 13C signals split due to 19F-13C coupling. Which carbon, chemical shift...

Arvin Moser
Characteristic isotopic patterns in MS can assist the elucidator in revealing the presence or absence of atoms. For the Br, Cl, S and Si atoms, a good approach is to examine the peak intensity of the A+2 signal. The respective contributions by the isotopes 81Br, 37Cl, 34S and 30Si are approximately 49.3, 24.3, 4.2 and...

Arvin Moser
Yes, it is possible to elucidate an unknown with just a 1H NMR spectrum but only for specific cases*. Case 1: an unknown with a low molecular weight and a “well-resolved” 1H NMR spectrum. Case 2: the unknown has been identified previously, or at least part of it, in a database/library/literature and a spectrum search...

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
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
The best use of a set of tools for a structure elucidation are those that have a general target or goal in mind. Random experiments for the sake of collecting data are a sure sign of inexperience. With that said, Infrared (IR) spectroscopy is a great tool for identifying or confirming a functional group(s). It...