Solid‐State ¹⁷O NMR Reveals Hydrogen‐Bonding Energetics: Not All Low‐Barrier Hydrogen Bonds Are Strong

Abstract

Abstract 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 17 O NMR spectroscopy can provide unique information about the energy required to break a LBHB. Our solid‐state 17 O 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.