Unprecedented Ultra-High-Resolution
Hydroxy Group <sup>1</sup>H NMR Spectroscopic Analysis of Plant Extracts
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Abstract
A general method is demonstrated for obtaining ultra-high
resolution
in the phenolic hydroxy group <sup>1</sup>H NMR spectroscopic region,
in DMSO-<i>d</i><sub>6</sub> solution, with the addition
of picric acid. Line-width reduction by a factor of over 100 was observed,
which resulted in line-widths ranging from 1.6 to 0.6 Hz. This unprecedented
resolution, in combination with the shielding sensitivity of the hydroxy
group absorptions to substituent effects at least up to 11 bonds distant
and the application of 2D <sup>1</sup>H–<sup>13</sup>C HMBC
techniques, allows the unequivocal structure analysis of natural products
with phenolic hydroxy groups in complex plant extracts