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ACD/Labs Blog

Arvin Moser
Due to their broad peaks and wide range of chemical shifts in 1H NMR spectra, exchangeable protons are known to pose challenges in NMR interpretation, but collecting 2D spectra and selecting proper experimental conditions can sometimes be used in our favor to learn more.

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
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
An HMBC experiment correlates atoms over a longer range from 2-4 bonds. However, it can also exhibit correlations for 1-bond separation. For a pure, unknown compound, the 1H -13C HMBC spectrum below shows three correlations to the carbon at 42 ppm. The correlations at 3.50 and 4.05 ppm correlate the 1H signal at 3.75 ppm...

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
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...