In the blog series entitled Distinguishing Impurities, several types of NMR experiments were outlined to offer some insight into what to be on the look out for. Although there is no set guideline in this process, the best advice I may offer is to keep track of all the solvents, be aware of the possibility for sample degradation or side products, and finally if a signal does not look right, trial and error may be the only safe bet to ensure nothing is overlooked.
Below is a summary of the each part in the series:
Part 1 covered the aspects a 1H NMR whereby 2 singlets seemed out of place in relation to the remaining 1H signals.
Part 2 described some prep work to check for differences in the integrals of the 1H signals.
Part 3 depicted a 1H-13C HSQC with no obvious indicators that any of the 1H signals were impurities.
Part 4 illustrated how a 1H-1H DQF COSY was a bad choice when dealing with 1H singlets.
Part 5 had a 1H-1H TOCSY spectrum lacking any long range correlations with the 1H singlets.
Part 6 explained how the 1H-13C HMBC lacked any correlation trails with the 1H singlets.