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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
The warning flag for this puzzle is evident in the intensities of the signals. For an unknown compound, the TOF-ESI+ mass spectrum below shows the expanded region around four isotope clusters at m/z 300.336 ([M+H]+), 322.307 ([M+Na]+), 599.672 ([2M+H]+) and 621.611 ([2M+Na]+). The intensities of the 13C isotopes (i.e. the [M+1] signal) vary between 40...

Arvin Moser
A key element in data interpretation is to identify any warning flags. Warning flags can help a chemist differentiate good data from bad data. For an unknown compound, the TOF-ESI+ mass spectrum below shows the expanded region around four isotope clusters at m/z 300.336 ([M+H]+), 322.307 ([M+Na]+), 599.672 ([2M+H]+) and 621.611 ([2M+Na]+). Are the intensities...

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
On the surface, both good data and poor data offer information about an unknown compound. The challenge is to differentiate between what is good data and what is poor data. The purpose of this puzzle is to examine some poor data. From an LC-MS+ TOF dataset, an unknown compound elutes at 2.86 minutes and spans...

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...