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ACD/Labs Blog

Arvin Moser
An HMBC experiment can be a key part in solving for an unknown compound. In this puzzle, ‘extra’ correlations add an extra degree of difficulty to its interpretation. For a pure, unknown compound, the 1H -13C HMBC spectrum below shows three correlations to the carbon at 42 ppm. Can you interpret how the correlations at...

Arvin Moser
13C-13C 1,1-INADEQUATE experiments offer a similar look to a 1H-1H COSY experiment. However, the INADEQUATE experiments do not have diagonal and off-diagonal peaks. The 13C-13C 1,1-INADEQUATE spectrum below shows 10 carbon atoms labeled C1 to C10. The pink lines connect the adjacent C atoms. There are 3 endpoints to the pink lines at C8, C9...

Arvin Moser
If there were an ideal NMR experiment for an unknown compound, many organic chemists would consider a 2D 13C-13C 1,1-INADEQUATE (Incredible Natural Abundance DoublE QUAntum Transfer Experiment) to be it. The advantage of this experiment is the 1Jcc interaction that directly correlates a C atom to an adjacent C. The drawback is the long acquisition...

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?