Proton shielding calculations in C<inf>6</inf>H<inf>6</inf>⋯H-CX<inf>3</inf>, X = H, F, Cl and Br, complexes

Abstract

The proton shielding constant and the shielding anisotropy of C6H6⋯H-CX3, X = H, F, Cl and Br, complexes were calculated as a function of the intermolecular distance at the density functional theory (DFT) with the PW91 functional and the Hartree-Fock (HF) levels. The changes of both quantities from their free molecular values among the complexes studied deviate from the average by 0.13 and 0.21 ppm at the DFT level and by 0.10 and 0.16 ppm at the HF level respectively for a short intermolecular distance of 2.8 Å and converge to the same value as the distance increases at both levels. The inclusion of the electron correlation reduces the changes of the proton shielding parameters but does not significantly change the standard deviation and the trends of the changes of both proton shielding parameters. The results confirm the long-range prediction that the changes of proton shielding parameters in C6H6⋯H-CX3 at large intermolecular distance are independent of the X group in H-CX3 and possibly due to the σ(magnetic) term which arises from the magnetizability of benzene.