For profiling phenolic compounds in plant extracts, 1H NMR spectroscopy is preferred over 13C NMR due to its sensitivity and detailed information on hydrogen atoms in the compounds. This allows for better identification and quantification of the phenolic structures present in the extracts.

It is nearly impossible to fully characterize phenolic substances in a crude extract using only NMR. You should perform pre-fractionation and isolate compounds of interest by column chromatography (flash-preparative LC). if your sample is pure enough to annotate meaning it contains purified phenolic substance both C and H NMR should be used. But H-NMR would be more elucidative.

The first thing is to purify the extract further with CC or PTLC, then the isolates can then be subjected to Hnmr if they are pure. And if they are simple compound they could be easily identified.