Solid-state 17O NMR reveals hydrogen bonding energetics: Not all low-barrier hydrogen bonds are strong,

J. Lu, I. Hung, A. Brinkmann, Z. Gan, X. Kong, and G Wu*
Angew. Chem. Int. Ed. 56, 6166-6170, (2017), special issue: 100th Anniversary of the Canadian Society for Chemistry.
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While NMR and IR spectroscopic signatures and structural characteristics of low-​barrier hydrogen bond (LBHB) formation are well documented in the literature, direct measurement of the LBHB energy is difficult. Here, we show that solid-state 17O NMR spectroscopy can provide unique information about the energy required to break a LBHB. Our solid-​state 17O NMR data show that the HB enthalpy of the O···H···N LBHB formed in crystalline nicotinic acid is only 7.7±0.5 kcal mol−1, suggesting that not all LBHBs are particularly strong.