Distinguishing between COOH, COO - , and hydrogen disordered COOH sites in solids with 13 C chemical shift anisotropy and T 1 measurements.

Since 1993, it has been known that 13 C chemical shift tensor (i.e., δ 11 , δ 22 , and δ 33 ) provides information sufficient to distinguish between COOH and COO - sites. Herein, four previously unreported metrics are proposed for differentiating COOH/COO - moieties. A new relationship is also introduced that correlates the asymmetry (i.e., δ 11 -δ 22 ) of COOH sites to the proximity of hydrogen bond donating partners within 2.6 Å with high accuracy (±0.05 Å). Conversely, a limitation to all proposed metrics is that they fail to distinguish between COO - and hydrogen disordered COOH sites. To reconcile this omission, a new approach is proposed based on T 1 measurements of both 1 H and 13 C. The 13 C T 1 values are particularly sensitive with the T 1 for hydrogen disordered COOH moieties found to be nearly six times smaller than T 1 's from COO - sites.