The chemical shift tensor for a strongly hydrogen‐bonded proton: The carboxylic proton in KHCH2(COO)2

The chemical shift tensor for the carboxylic proton in potassium hydrogen malonate has been determined from a proton multiple pulse experiment carried out at 270 MHz. Both the values of the averaged chemical shift relative to tetramethylsilane (TMS), ?=−20.5 (5) and the chemical anisotropy, Δσ=27.6 (6), are consistent with the very strong hydrogen bond found for the carboxylic proton in KHCH2(COO)2. The directions of the eigenvectors are similar to those found for proton chemical shift tensors determined for other hydrogen‐bonded systems, i.e., the z‐principal axis is fairly close to the O⋅⋅⋅H⋅⋅⋅O vector off by 9 (2) °, and the x‐principal axis is close to the normal of the plane defined by the carboxylic groups [off by 8 (2) °].