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ACD/Labs Blog

Arvin Moser
There are many variants of 1H-13C HSQC experiments that can used for elucidating unknown molecules. In particular, band-selective HSQC data can assist with the data interpretation of correlations with regions exhibiting ambiguous assignments.1 For the following unknown compound, two 1H –13C HSQC spectra were collected. Both datasets (bsgHSQC and gHSQC) were processed with the same...

Arvin Moser
In collaboration with Sequoia Sciences Inc., we developed a strategy for the dereplication of a complete or a partial structure using 1H NMR, 1H–13C HSQC and 1H–1H COSY spectral data, a molecular formula composition range and structural fragments against a massive database of about 22 million compounds is considered. The work was based on 18...

Arvin Moser
An HSQC-DEPT experiment shows one-bond correlations. The CH and CH3 groups are generally phased positive (red) and the CH2 groups are phased negative (blue). For the following known compound, the 1H -13C HSQC-DEPT spectrum (collected at 150 Hz coupling constant) below shows a negative correlation (blue) at 2.72 and 61.1 ppm with a 1H integral...

Arvin Moser
A key step in being a successful elucidator is to understand the principles behind the experiment. Below is one such case. For the following known compound, the 1H -13C HSQC-DEPT (or multiplicity-edited HSQC) spectrum (collected at 150 Hz coupling constant) below shows a negative correlation (blue) at 2.72 and 61.1 ppm with a 1H integral...

Arvin Moser
Hybrid experiments, like an HSQC-TOCSY experiment, add an extra dimension to its interpretation. It is through practice that one can become familiar with interpreting the data easily. For an unknown compound, a 1H -13C HSQC-TOCSY spectrum was collected. There are 8 visible HSQC correlations circled in red and 10 TOCSY correlations circled in blue (numbered...

Arvin Moser
Depending on the mixing time, HSQC-TOCSY experiments generally offer information on both short-range and long-range coupled nuclei. The issue arises in sorting out the HSQC correlations from the TOCSY ones. For an unknown compound, a 1H -13C HSQC-TOCSY spectrum was collected. The expanded region of the spectrum below shows several correlations. How many HSQC-related correlations...

Arvin Moser
With any experimental data, producing a list of scenarios that are consistent with the data can help guide an elucidator through the problem while ensuring nothing gets overlooked. For an unknown compound, the 1H -13C HMQC spectrum shows a CH group with a correlation at 7.0 and 113.0 ppm. Is the carbon hybridization an sp2 or...

Arvin Moser
Part of the process of interpreting data from 2D NMR spectra is to adjust the intensity threshold in order to differentiate visually the signals from the noise. A certain level of cautious peak picking is needed so not to overlook a weak signal nor confuse a noisy region for a real signal. For an unknown...

Arvin Moser
Spectral data that exhibit weak signals (low S/N) can easily be misinterpreted. A good approach is to check the data against other data to confirm whether the signal is real or an artefact. For an unknown compound, the 1H -13C HSQC spectrum below is shown at two different intensity thresholds. The aromatic protons at 6.97...