The change of the proton magnetic shielding in red- and blue-shifted linear hydrogen-bonded complexes

Abstract

The change in the proton magnetic shielding constant of FH and FArH on the formation of the vibrationally red-shifted FH... Rg and blue-shifted FArH... Rg (Rg = Ne, Ar). complexes was determined by GIAO ab initio computations at various levels of theory. The blue-shifted FArH... N2 and red-shifted FArH... P2 complexes were also studied. The characteristic downfield shift of the isotropic proton magnetic resonance in red-shifted hydrogen-bonded complexes is smaller in the blue-shifted complexes. In FArH... Ne and FArH... N2 the proton NMR actually shifts to higher fields on complexation. These results are rationalized by considering the changes in the magnetic and electric contributions to the proton shielding in FH and FArH.