Are Ring Currents Still Useful to Rationalize the Benzene Proton Magnetic Shielding?

The conventional interpretation of proton NMR chemical shifts is supported by large basis set ab initio quantum mechanical calculations. The benzene protons are predicted to lie within the deshielding zone defined in terms of the out-of-plane magnetic shielding domain. However, ring currents by themselves are not sufficient to account quantitatively for the observed benzene proton downfield chemical shift. σ-Electron contributions must also be taken into account. The conventional explanation for the ethyne proton chemical shift is valid.