Proton Shielding in the Bihalide Ions

Abstract

The absolute proton shieldings of the bihalide ions, FHF−, ClHCl−, BrHBr−, and IHI−, are consistently about 14 ppm less than those in the corresponding gas‐phase hydrogen halide molecules. It can be shown that in both species, the dominant contributions to the shielding are all proportional to the hydrogen charge density. Thus, the charge density in each ion must be less than that in the corresponding molecule, consistent with SCF calculations on the bifluoride ion. This is the charge shift predicted by a simple electrostatic model, but not by the independent‐electron MO model.