¹ H‐nuclear magnetic resonance study of a soil humic acid

Summary The structure of a humic acid from a New Zealand pasture topsoil has been investigated by 1 H‐n.m.r. spectroscopy. The work complements a recent 13 C‐n.m.r. study on the same humic acid. Irradiating the water peak in the spectrum greatly improves spectral quality. The results show that the proton aromaticity of the humic acid (excluding exchangeable protons) is 17%. Considerable amounts of protons in the humic acid are associated with carbohydrates (35%). Useful structural parameters describing the average molecular structure of the humic acid were derived by combining both 1 H and 13 C data. Further work is needed to determine both the percentage exchange of protons in alkali and the percentage of inorganic hydrogen in humic acids, before the condensation and the degree of substitution of aromatic rings can be quantitatively estimated.