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ACD/Labs Blog

Arvin Moser
Coupling constants from a 1D NMR spectrum can be very useful to a chemist when trying to characterize a structure. However, there are cases where the perceived coupling constants can be misleading and thus wrong. The 1H NMR spectrum below shows several multiplets for a major component tryptophan and a minor component. For tryptophan, the...

Arvin Moser
Many analytical data rely on common calculations. This puzzle covers one such common calculation. NMR and MS data were collected on two unknown compounds. The TOF-MS data shows the [M+H]+ at m/z 300.0000 and 600.000 at an error of 0.001 Da. The 500 MHz 1H NMR spectrum shows two chemical shifts at 1500.00 and 3000.00...

Arvin Moser
Logical reasoning and pattern recognition form the basis for making a pattern-to-fragment connection. For an unknown, the 1H NMR spectrum below shows 5 multiplets in the aromatic region. The multiplet at 7.57 ppm shows two overlapping multiplets: a broad signal overlapping a ‘doublet’ (noted as d*). Based on the multiplets’ tilt/lean and integrals, a 1,2-disubstituted...

Arvin Moser
An experienced elucidator can recognize spectral patterns and use this information to piece together a fragment. This puzzle examines one such pattern-to-fragment connection. A 1H NMR spectrum below shows the aromatic region for an unknown compound? Can you identify the fragment that would produce this pattern?

Arvin Moser
Quaternary carbons can be tricky in identifying. Keep your options open to ensure the bigger picture is not missed. The expanded region of the 13C NMR spectrum shows 4 signals for an unknown compound. The signal at 172 ppm represents 1 or 2 amide group(s). The higher intensity of the signal at 172 ppm in...

Arvin Moser
Spectral data is just data until you can see the bigger picture. This puzzle looks at a scenario of quaternary carbons. For an unknown compound, a standard 13C NMR spectrum (500 MHz CDCl3) was collected. The expanded region below shows 4 signals. Is the signal at 172 ppm attributed to 1 or 2 carbons (from...

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
A key step in interpreting NMR data is in counting correctly the number of signals associated to the compound of interest. This puzzle covers one particular example. For a pure unknown compound, the 13C NMR spectrum below shows several 13C signals at varying intensities. What is the minimum C atom count?

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...